OMG- I HAVE THE PERFECT THING FOR YOU!!!!! I use these myself, and they are AWESOME!
The seller is Shel, now... she doesn't have them listed on her site right now. But, I JUST SPOKE TO HER and she has them in stock...
They are glue dots that are 1/2 inch circles and NON PERMANENT, but hold really well, until you WANT them to come off. They mess up nothing and leave NO residue. It is what they use in museums a lot too, from what i understand. She said you could contact her and she will talk to you about them, how many and how much, etc. PLUS, she is one of the BEST etsy sellers I have EVER dealt with!
It is on this site:
http://www.etsy.com/people/suppliesbyshel?ref=owner_profile_leftnavIf you want to go to my FaceBook artist page and see one in action on a card, take a look here:
https://www.facebook.com/photo.php?fbid=485644881445810&set=pb.279238488753118.-2207520000.134956959...and
https://www.facebook.com/photo.php?fbid=485644858112479&set=pb.279238488753118.-2207520000.134956959...These are magnets on cards, using those things! ;)
Good luck!
Blue