Seen him in Bruges too a few times. This would be fun i think, tho a little weird too since he would never approve of it.
You could also make it about playing him. Then it wouldnt really be a game but more of an experience on what it is to be homeless. A game of life where you can't do much. Where a bunch of npc's stare at you.. Maybe get the guys from "ghent theft auto" to give their map to this project so you can actually walk around a massive map of ghent, and be bored, like him.
But then there should be easter eggs or something, random events, as i'd imagine that happens a lot too if you are on the street a lot. you see a lot of weird stuff. But you can't do anything about it. you are the unseen guy that everyone knows.