Any agreement is fine as long as both parties intend to honor it. If you think you're going to appeal to the state, I don't see you having any luck with 200% interest rate. I'd suggest adjusting the terms on whatever is owed to you, in exchange for some sort of additional security. Perhaps interest only payments (at a very different rate) with 18 month balloon would give him enough time to get it in order, and protect the principle for you.
One option that I hesitate to recommend, but I've seen used in a particularly harsh situation, is getting a judgement, and attaching it to a pet. I don't know how I feel about this, and I think I'd only consider doing it if I felt considerably wronged, but it has resulted in motivation where all else failed, when the pet was taken away. Obviously, if the person doesn't care for their pet, this won't inspire them much.
If you work together, there is almost certainly some other arrangement that can be made to satisfy the debt.
Good luck!