I never really had an issue switching to F/T, but here is a few things to try. I take the mouse out about 9am. I let it sit out till about 2-3pm, then I get some hot water out the sink, I put the mouse in the water(The mouse stays in a ziplock bag the whole thawing process) then I sit a glass full of hot water also on top of the ziplock bag to keep it submerged under water, I let it sit in there till the warm gets luke warm, then it's usually good to feed. The mouse is warm, its fully thawed out, then I hold the mouse by the tail and wiggle it in front of my Annie and she snatches it up then chokes it. Try that see if that works for you, make sure its fully thawed though because im sure our house temperatures are different. If that doesn't work then you can try to rewarm the mouse in warm water and try the leaving in a dark paper bag. I'm pretty sure the wiggling the mouse in front of him will work though as it will make him seem live.