You have to SBF back to FroYo and then install the .602 update available in the TBH app. This is not an easy process, but it's safe.
Follow the instructions below up to the part where it tells you to install the 2-part rooted .596 GB. Instead, install the .602 update from the TBH app. After that, if you want, you can install the LGB 0.x zip (reports say they're compatible) or you can stop with the .602 update. http://www.droidforums.net/forum/li...-1-stock-apex-cm7-etc-any-rom-liberty-gb.html
If you don't have the TBH app, too bad, so sad, you have to wait until P3Droid decides to make the rooted .602 update publicly available.