guessing you didn't have anything written up in a contract? all verbal?
yeah, 5k isn't chunk change. I understand you not wanting to call him out and risk the chance of possibly loosing the funds. The only thing I could think of is to threaten to out the guy nicely at first. Then harshly, then pull the trigger. pinball is a relatively small community, maybe the mear threat of outing him would be enough to get him to get off his ass and do what you two agreed to.
good luck