There are some games we can never get enough of, and Super Mario Galaxy 2 definitely fits in that category. Unfortunately, Nintendo isn't the type of company that releases a lot of DLC (which you can argue is a good thing, of course).
At least the Wii is easy to hack, right? This is a trailer for a mod called Super Mario Galaxy 2, which requires a copy of Super Mario Galaxy 2 to run. Not that Nintendo condones this sort of thing, but we can't really see the harm, especially if you have to buy the game to play it.