hmm I've never actually seen anyone groom a Rex coat other then using a fine mist and their hands to remove stray hairs and prevent static. Unless the Rex has the fur to begin with then there really isn't anything you can do to improve it without it being considered altering the coat, which can get you tossed from the show room.
I have seen people use mane N tail on rabbits (Big No-no)
Witch Hazel I have seen people use, and you can use because it will evaporate before you can even get the rabbit on the table.