Please read:
http://en.wikipedia.org/wiki/Regional_lockout
To answer your question: not without someone with considerable technical skill taking apart your Wii, voiding the warranty, doing some unsupported soldering and modifications to it which have a high-probability of destroying your Wii if he doesn't get it perfect, and could still kill your Wii later if Nintendo ever puts code in a game to detect it.
Such "modifications" are not advocated or supported on this forum, and strongly discouraged. Discussions about details of them are closed and users often banned, since their primary use is for illegal purposes.
Your son made a purchase mistake, and there's no free way out. The game might as well be for the Playstation. You need to suck up your losses and just buy the correct game. You could probably sell the US one on eBay for a bit and get some money back, but you're still going to lose some money in the process regardless.