Stock photo - model release?

Okay, well I never really submitted a photo for stock that contained a person in it before, but I may start doing so.

What am I supposed to do with model release though? It seems each site has one, and I am not going to make someone sign like 4 of them just so I can submit to 4 websites...

Surely people submit their photos of people to more than 1 stock site -- what do you guys do about this?

As long as you have the original signed document, publications and stock agencies should be satisfied with copies.

I don't really have any experience with stock agencies, but I make it a point to include a scanned copy of my model releases on any image discs I create and send to publications, clients, model agencies, etc.