When I have had to wean off of critical care, I've done as your vet said, and added pellets to the CC. I don't crush them up much though. Maybe the first couple times, and that's only going to work if he'll take his CC out of a bowl or off a spoon. It doesn't work so well when all he will do is eat out of a syringe.
How is he eating his CC? If he's eating out of a syringe, try and get him to eat it off of a spoon. After you can get him to start eating it that way, try coarse grinding his pellets a bit and adding them to the CC. Then try and get him to eat it out of a bowl. Once he's doing that you can start adding larger and larger pieces of pellets and slowly easing off of the CC.
Will he eat hay?
How is he eating his CC? If he's eating out of a syringe, try and get him to eat it off of a spoon. After you can get him to start eating it that way, try coarse grinding his pellets a bit and adding them to the CC. Then try and get him to eat it out of a bowl. Once he's doing that you can start adding larger and larger pieces of pellets and slowly easing off of the CC.
Will he eat hay?