Originally Posted by BustaUppa

Are people here familiar with the Rock Band Harmonies Project? It's a method of adding harmony charts to pre-RB3 songs. I gave it a try yesterday and it actually worked!! So far the RBHP community has charted all the disc-based songs (RB1/RB2/Lego), along with a decent chunk of DLC tracks.

I don't quite get how it's possible but it utilizes a song cache built off of a modified save file. I can personally verify that it works without any type of modded Xbox. If discussion of this is considered against the rules I'll remove it, but it doesn't involve custom songs or the use of any DLC that you don't own already, so I think it should be alright. I plan on writing a more detailed CAG blog about it, but the link above gives instructions and everything.
**EDIT: it's for Xbox only, unfortunately