This is my exact problem with most bi male characters. It seems that often the reason is "I look beyond gender" (Anders...) or that "sometimes, but I prefer women" (Zevran and possibly Bull). But what are we gonna do?
Yeah, a summary of bisexual guys in Bioware games:
Sky (JE) - widowed with a child; approaches the male PC about why he isn't interested in the ladies; surprised by gay male PC, but eventually shows interest
Zevran (DA: O) - "promiscuous bisexual"; strong female preference; some interpret that the story implies that he 'became' bisexual because of his work
Anders (DA 2) - "retconned controversy"; strong female preference in DA: A; might be pansexual ("I fall in love with the person, not the body")
Fenris (DA 2) - no mention of his sexuality at all; ends up sleeping with Isabela if not romanced
Kaidan (ME 3) - "retconned controversy"; strong female preference in ME and ME3 (he likes asari alot)
Bull (DA: I) - "promiscuous bisexual"; actually pansexual; slight female preference; BDSM romance; ends up in a relationship with Dorian if not romanced
To be honest, because I feel that, outside of Sky and Fenris, the bisexual male LI's are either "promiscuous bisexuals" or "retconned straight guys", I'd much prefer to see a KISA be gay. I was originally on the fence about it (and, to be honest, would still be thrilled if we got a bisexual male KISA), but the more I think of it, the more I'd like to see a KISA be gay. I think that if a KISA were to be bisexual, people would just write it off as "fanservice" and view him (even if he were an original character) as written to be straight, but "made" bisexual because of this thread. And, to be honest, I'm not confident that the writers would write him in a way that wouldn't make it seem like he's "straight except for PC", particularly given that they wouldn't be able to draw on the 'promiscuous bisexual' trope.
If they did make a male bisexual KISA, I'd really like him to have a strong male preference, just to break the cycle that male bisexuals really like women, but will be "gay for PC". If they made him a chivalrous knight type, I think it could work.