I use a plastic spudger tool. You can get one from iFixit for $2.95:
http://www.ifixit.com/Tools/Spudger/IF145-002
Shove either the sharp end or the flat end and move it up/down and around the key fob until it starts to give. Using a plastic tool like this doesn’t cause scratches and is usually softer than the key fob material itself.
