Depending upon the implementation of mimic_bot, this is a quiny approach. mimic_bot obviously can't run the opponent on an exact quine of yourself, because then you won't achieve mutual cooperation. (When one of the bots cooperates unconditionally, the other will see that it acts_like_cooperate_bot and defect.) So long as mimic_bot plays opponents against a pure MimicBot instead of a perfect quine, this should work quite well.

On an unrelated note, woah, how'd you get whitespace working?