Depending on your network setup (the method you're using to share the internet connection), you should be able to tighten the belt on his connection from your own machine. Though, I couldn't tell you HOW to do this.
If you want to install software on his computer, look into the program
NetLimiter which will limit the amount of bandwidth a program is entitled to use. The only option it's lacking is limiting the net bandwidth the machine is allowed to use.
The program doesn't appear to have any password lockout, so you'll just have to insist that he doesn't monkey with the limit, else lose his access.
- Raccoon
