I don't mean this to sound dumb, so if it does, I apologize in advance.
I always hear this behavior should be avoided, discouraged, etc. I'm not sure if I agree with that. What I mean is...obviously, they are trying to satisfy some impulse. Does denying them that release harm them as well?
Other than being embarrassing to us (oddly enough, only after we know what it is...before, it was funny and cute), what harm can it do? I guess maybe a female might waste a lot of nutrition producing infertile eggs, or risk getting egg-bound. I figure if they're already bonded enough with you to want to try to mate with you, they've already made you their mate, despite them "sealing the deal" being impossible.
I can safely say, as a human male, I wouldn't want to "join a monastery" so to speak.
Just trying to see it from their point of view, and keeping an open mind.