Yes, I would try to keep him on the prey he is used to for a week or two, then I'd try to change to a slightly bigger rat weaner. Small weaners are 25-50 gr, medium weaners are about 50-80 gr, then you go to small rat 80-150. Those are the weights more or less, as they vary from supplier to supllier and they might have different names.
Talk to whoever supplies you the food and ask what are the ones he sells and how much they weigh
;-)