In the majority of the "straight to gay" yaoi I've read, the guy who was straight ends up being the Seme.

What I'm looking for is Yaoi where the straight guy ends up as the Uke. He NEEDS to be completely straight and NEEDS to be at least a little shocked or resistant to the idea of being gay. None of that "Oh, I guess I'm gay?" stuff. I'm straight and haven't "turned gay" before, but I can pretty much guess that it'd come as a surprise.

Something like Koisuru Boukun - Guy is straight (homophobic actually) and is the Uke.

What I'm looking for doesn't need a homophobe in it though.

Feed your head.

Rakka Sokudo

Agh, that's the only one I can remember right now that fits the situation exactly. I'll reply back if I find something else...>_<;;

You can, you should, and if you’re brave enough to start, you will.

I'm not your steppin' stone by Kano Shiuko
The guy was previously in love with the seme's sister

Arashi no Ato
Sorenari ni Shinken nandesu.

I have the simplest tastes. I am always satisfied with the best.

• Oscar Wilde -

Kyoushi mo Iroiro Aruwakede

this might help~ http://www.mangaupdates.com/series.html?category=Straight+Uke&orderby=rating

The Cornered Mouse Dreams of Cheese I loved it, and I think it fits perfectly with your request. The straight guy begins being the uke amb ends being both uke and seme

ELEKTEL DELUSION, The UKE is Straight, his bestfriend is Gay they grew up together, and got jealous when his bestfriend said his gay and dating a guy, so he got curious coz he thinks his handsome that it has to be him.