Small Claims Court could be a good hammer to use in this. Being in the same state, it should be easy to get a judgment enforced. Since he is 4.5 hours away, he may just settle with you to avoid having to drive all that way (maybe more than once!) and if he does not show, you may get a judgment in your favor by default. (My understanding is that is how it usually works but I don't have a lot of experience in SCC -- only a little -- one was settled before and the other after an adjournment after the judge orders the original contract writer, who was in Texas, to appear -- this was in New Hampshire)

It is definitely a good hammer since most people are afraid of courts etc and won't want the hassle.