You can get old mouse bedding ( maybe from a pet store) and let your rat defrost in it and hang in it for a while so that the mouse scent will linger on the rat. Not much else to do until they make a colonge of " Ode to mouse"

I have a bp who does the same w/ rats and I tried everything. I gave up and just buy jumbo mice from rodentpro ( about 35-45 grams) and fed two or three.
Good Luck