The only issue with what voteDC has recommended is that Saints Row 2 won't play once you do this. Having been in the same position you have to find another player with the same pack(s) as you. Deleting your pack from the console will cause an error message
when you attempt to load the game, and will force you to create a new save unless you reinstall the content by downloading it again. If he has a friend who he wants to play Saints Row 2 with, the only real option is to try and persuade that friend to download
the content packs you have. Off the top of my head, the three packs are the
Unkut Pack, Corporate Warfare, and Ultor Exposed. If you have only the Unkut Pack installed, you're in luck: the entire pack is free and therefore it won't cost any of his friends to download. The other two packs are
800 Microsoft Points each, so I recommend being absolutely certain which pack you have before any friends download them, unless you make a mistake which could be rather costly.