Oh, I know it's not too late to get him on rats, lol. The only reason I offered him a mouse tonight was because during feeding night for my other BPs I thawed their rats right by his tub to see if I could get a reaction.. nothing. The second I brought the rats near my Normals' tubs they went "hunting". The only reaction from scent I've been capable of getting out of Seeley was from the mouse today. I'd rather have him on mice than nothing at all.
So, when I purchase the Rat on Sunday I'm going to have them toss in a little used aspen from a mouse tub. Considering he was on live small rats for the majority of his life, I'm not worried about him becoming a "mouser".