Buy new ones or paint them while they're on your car. The backing is a 3M tape that once removed can't be reused and it's a lot easier and faster to replace than it is to scrape the tape, cut and reapply new.
To get them off I use a strong fishing line, have used dental floss in the past in a pinch too. Take a few lines and saw through the tape. There is a pin on the back of the snake that helps position the emblem to the fender so you'll need to saw from the top and then saw in from the bottom. Once about 3/4 of the tape is sawed through you'll be able to gently pry the emblem off.
some fishing line and heat them up a little with a hair dryer or heat gun (be VERY careful not to overheat the paint) and run the fishing line behind it then roll off the residue with your finger tips and finish up with a little cleaner to remove whats left.
+1 on fishing line. I actually have used a plastic razor blade and a hair dryer on low to get off the majority of the gunk, then clay bar to pick up the embedded stuff.
and then how about putting the snakes back on after you take them off? tape? got the car painted and they put the snakes on backwards and i dont wanna take it back to them because they were a pain in my ass.