How frustrating. Remember you ultimately want him to shrink up and go away. So your action should not escalate things - as many people suggestions would be like throwing gasoline on a fire.
I had an employee that suggested we substitute something important with something less expensive and just not tell our customers. In addition to being illegal, it was immoral and was the last straw with that employee. I ended up giving her a bunch of credit and she is still a customer.
How about offering to give the guy a free sandwich every Monday for a while? You could offer to help feed him while he is looking for a new job. He would be away from the restaurant most of the time - and you would know when he is coming. Plus it could be considered a nice thing to do.
And hopefully, he would only come in a couple of times.
edit: PS Bonus - if he comes in the second week - make sure it's packed as a 'to go' meal.