It's possible. First of all, the safe sex (amongst boys) that requires a condom the most is anal. Let's talk about that first.

If you want advice based on the KISS principle ("keep it simple, stupid"), which actually works best in the real world, then the advice is 'always use a condom for anal sex.'

If you want to go into detail, here's the scoop. What Dakota says in the other answer so far is theoretically true but considered to be impractical. Yes, two partners getting together could both get an HIV test, and then repeat it a couple of months later, thus showing themselves to be HIV-negative. Then, if they were monogamous, they could theoretically have condomless anal sex. The only problem is the "if" in the last sentence. History has shown over and over that people who agree to be monogamous may yield to other impulses, especially when they are young men, especially when they are travelling, and especially when they have had some alcohol or other druggy things. Classically, they then get infected (sometimes via an uncommon route, like condom leaks) and bring the virus home to their partner. Again, classically, they are afraid to say they've been having some on the side, and perhaps they regret it and vow never to do it again, but they don't realize the viral damage has been done. So ultimately both 'monogamous' partners go down to HIV, one feeling guilty, the other feeling betrayed.

There's actually an alternative to this, which is to have a monogamous relationship that is also an "always tell" open relationship. What this means is that both partners expect to be monogamous, but they promise each other in advance that if anything else happens, they can always tell each other with a guarantee of no reprisals or heavy emotional punishment. Then if one person falls off the monogamy wagon, he can tell the other what has happened and they can decide together if they need to re-test their HIV status (a process that can take some months, as infection at first doesn't produce diagnostic antibodies or detectable 'viral load,' and the viral load test isn't automatically done anyways). This is a little more risky than "always use a condom" but it doesn't impose the level of blackmail against honest admissions of sexual (mis)adventure that classic monogamy does. Some personalities might not be able to handle this, either because they would become wounded by having their partner do something with another person anyways, or, oppositely, because they would interpret their liberty as a license to be promiscuous. Some delicate negotiations are needed to see what a supposedly monogamous, always-tell open relationship would actually bring. It's a whole lot easier to just use a condom. Anyways, condoms can be fun, and they're certainly clean, and for some people they're even a fetish. They may allow prolongation of pleasure. They're not by any means just an encumbrance.

When reckoning who might already have HIV, you have to think a few unpleasant thoughts: a virgin who's had a botched medical procedure might have it, even without his knowledge. Someone who's used injection drugs and really doesn't want to tell you about it could be HIV+. He could be a virgin, too. Someone who was raped could be HIV+; it might even have happened years ago. The person could have a mental block against thinking about it and may believe himself to be a virgin, or at least, desperately want to live as if he is one. In safe sex, you always have to think that a person may lie to protect their feelings. People actually lie constantly about matters related to sex and sexual feelings -- I am sure you do it routinely to survive as a boylover, if you hang out with friends who like to converse about hot girls. Because not getting HIV is so very important (it's a gruesome way to go), it's advised not to take anything anyone says at face value. Unless, as in the open relationship example above, there's no disadvantage whatsoever in being honest.

I did know a bisexual boylover who died of AIDS at 16 after having had a single unsafe sex act with a girl who'd been abused by a foster dad. He was a very sweet young friend and I miss him greatly. All the rare events in medicine happen routinely, even though rarely. Nothing is so strange that it can't happen to you.

Turning the body around (lol), the risk of HIV transmission via oral sex is quite low, so if two partners have a reasonable belief that they're HIV-negative, the world is their oyster (or cucumber puree, if you're vegetarian). Sorry. Mutual j/o is zero-risk no matter how you do it. Kissing isn't a problem but I'd go to a clinic and get advice about anything to consider if I was going to take up with an HIV+ partner. Canker sores in the mouth or oral cuts may make it ill-advised, but I'm not up on the latest statistics about that sort of thing. Also I'd seek advice about oral sex with an HIV+ partner or someone who's had some sexual experiences and can't be sure.

If you have a headache now, just say 'forget all the details' and use a condom for all anal sex. And be careful - breakage is possible with rough use and leakage with clumsy use. I lost another dear person to a condom rupture.

I am sure that our celibates are wondering why anyone would go there, but fact is that there are many people for whom absolutely nothing says "I love you" the way this sex act does. And it otherwise does a beautiful job of scratching the "it's better to marry than burn" itch among loving partners.