Just tell them they're not your type or that you're not interested...or that you already have a boyfriend/girlfriend. Anyway, what kind of hot are we talking here? I've found that generally an attractive male will make an equally (or at least close to) attractive female, so it could actually help you in the end if you care about that stuff at all. Either way, you need to tell those girls to back the hell off.
But yeah, I totally get what you mean by hating yourself afterwards and feeling guilty and whatnot. For example, I'm built to be physically strong (even though I don't work out), so I often am asked to lift heavy stuff and then get compliments like, "Oh, what a strong young man!" Things like that make me pissed at first, followed by the guilt of wasting the potential of my masculine body by wanting to be a woman, similar to you if I'm not mistaken. You're definitely not alone in that department.