I have always used hairspray (Aqua Net Extra Hold!) for installing / removing m_______n bike grips, which are similar to Grab-On, er, grips. I would imagine it would work fine for what you want to do. The beautiful thing about hairspray is that it's a solvent and a light glue. It will loosen whatever stickum is holding those grips on your bars, and then when you install Grab-On grips it will provide stickum.
In the happy afterglow of the season's first road race,
Morgan -- Morgan Fletcher, morgan@hahaha.org Oakland, CA