I know this sounds crazy but I've been using this for 15 years both on MC's and Mtn. Bikes.... Aqua Net Hair Spay! You just spray the crap outta the bars and slid on the grips. Then its slippery as heck so you can rotate and position your grip. It does take at least a day to dry up but once dry, its strong as anything. If you ever have to take the grip off, you start by spraying the end of the grip and slowly lifting and working it into the grip with a small screwdriver while continuing to spray it in.
Now that I'm writing this, I realize all my grips have been rubber to metal so this might not work on metal to metal.... oh well.
Thanks for all the replies... I had heard about the Aqua Net thing... pretty cool. As for removal, I just use my air compressor with a high pressure tip and start at one point and go all the way around the grip and it breaks the glue.