what exactly is it your sticking? Just asking, because whether it's to be permanent or not makes a difference.
I have my plates stuck on with double sided mega strength velcro - it's literally for industrial use - you can stick it to the wall and velcro hammers and stuff on to it - but I did that because I knew sooner or later the private plate would need to come off and as it's stuck direct to the bumper I can pull it off and 'velcro' another one on if I have to.
I got that off ebay - you can get all sorts of little stuff like you want on there - cheaper and quick delivery as well. Have a look.