If you do try the f/t silversides, make sure to try ones that the heads haven't broken off of. This sounds bizarre, but I have two snakes that absolutely will not touch a feeder (mouse or fish) if they can't find the head. It's like it just blows their little minds or something and they don't recognize it as food.

EDIT: Safe fish list is about halfway down the caresheet

http://www.thamnophis.com/index.php?page=caresheet