when switching my lesser from live mice to frozen, i tried to make 'lifelessness' the only variable changed... so dry thawed and fluffed up like a live mouse, same color and then i use tongs to simulate the way a mouse moves when its dropped into her enclosure. i find you have to do a little song and dance for them -- they dont recognize a flopped out mouse as prey... its not moving... see if that helps. If the snake is a bit bigger, just try offering f/t and if its refused wait til next feeding day and try again. the other thing you can do is rub the ft rat in rat shavings, to make it smell a bit more 'genuine'.

good luck!