I finally was able to do some custom songs on GH2. Its not that bad, you really just need the mp3, a midi and a chart file for the songs, the later of the 2 can be gotten from scorehero.com
There is also software that will inject the songs into the main file for GH2, making it painless, after that test and reinsert the .ark file into the iso and its done
it took a while to make everything sync up, adding and removing silence to some songs, once i get used to how everything works it should be a breeze to do.