I don't know if you've tried this, but it has improved my little ones feeding response in the short time I've had him. At first, he would take prey but not be super interested, now, I just dangle the rat in front of his hide and he strikes like his life depends on it.
I thaw the rat pup in a ziplock bag put into a tupperware of warm water for about 10-20 minutes. When I take it out, it's still slightly cold. After this I put the rat just to the side of his che to warm it to body temperature. This also gets the smell going through his enclosure, which I think is the reason his response has gotten so intense. After about 10-15 minutes under the CHE, I make sure the rats belly is soft and the head is warm to the touch, even better if you can measure the rat temp with a thermometer and shoot for around 100 degrees. After that I just take the rat with my tongs and shake it a little bit in front of his hide. Even if hes shoved way in the back of it, not even looking at the rat, within about 30 seconds hes struck and coiled and back in his hide.
The combination of the smell permeating the enclosure and the rat being warmed to body temperature has done wonders for me.