The Rowing Machine for Wii is a cheap-looking rowing machine that has a spot for a Wiimote in the handlebars. It should make playing Super Mario Galaxy 2 next to impossible.
Apparently it'll work with a couple of the mini games from Wii Fit and Wii Sports Resort. But I'm gonna go ahead and guess that those few rowing-based games aren't suddenly going to get a lot more entertaining when you're using a more elaborate piece of equipment. But hey, if that's all you need to get motivated to work out, more power to you.