I don't see how he's gonna be caught/tracked in Boston. There's 20,000 people, he'll wear a disguise, and his bib number WILL NOT be visible before the start. How are you gonna find this guy? He may even hide out in a slower corral. Finding a friend that you're looking for there involves luck, finding a sneaky person that doesn't want to be noticed is next to impossible.
I've said it before - this guy is a ghost. He's beaten me in races (raceS, Plural!) that I had a faster 1/2 split than him at and didn't get passed by any runners afterward.
I think the best way to prevent him from cheating in Boston...again is to prevent him from getting into the race. Contacting the BAA or getting his BQ time stripped seem to be the most logical ways to do that.
I think he's more likely to be spotted at a smaller venue. Unfortunately, the smaller races typically have less safe guards in place to prevent cheating. And in most cases don't have a public list of entrants. I have a pretty good idea of which races he'll show up at if his goal is still to cheat his way to a sub 3 in every state as a masters.