"Thou shalt not lay with a man as thou would a woman."

But, if you're a gay man, you wouldn't want to lay with a woman.

So, if you have sex with a man, it wouldn't be "as thou would [lay with] a woman," since thou wouldn't lay with women in the first place.

So, see? It was never a sin!

(Gets more complicated when you're bi, but I think if you only bottom for men and top for women- or vice-versa- it probably still works out)