I don'tthink there's a way to do that. There is however a singstar type project that was started up for the computer but I forget the name of it. You should be able to find it. The DRM for the songs is fairly tough/draconian so you won't be able to find any way to be able to transfer songs.
As it is, if your PS3 dies, it takes an executive order to get songs unlinked from your dead ps3 so you can redownload them on a new machine.