You said that you want him to jump rabbits for you. I'd just get him out in the woods alot where there are rabbits. I doubt very much that any terrier is going to run rabbits like a beagle but they surely will search them out and roust 'em for you. These Rat Terriers hate any kind of furred critter.
When he was young my dog would go after most any furred game, but had a natural treeing instinct. So I would praise and encourage him on squirrels, while discourage him from treeing 'coons, chipmunks, etc.....
My dog is really from a long line of Treeing Feist squirrel dogs, but this line has the Rat Terrier traits because the breeder would line-breed and when the breeding started to get too close would use a Rat Terrier as the out-cross dog to bring in new blood. So my dog is 1/16 Rat Terrier, being that many generation away from the out-cross.