I used to do this pre-Rocksmith, had all the GH/RB games, used to put the game into training mode, then rip the song from my PS3 to PC using the line in, export it to MP3, then you have an isolated track to play along with :) Was disappointed when RS came out to find they weren't proper mutli-track backing songs. Being able to download all the mutli-tracks much better than recording them one at a time :S