Use an air compressor and just get under the grip and move it along inch by inch.
And if you don't have access to one, there's another way that I haven't used that seems pretty sound though. Get several zipties and put them in your grips so they would be in between your grip and the bar. slide the grip on and the zipties will slide along the bar easy, then once the grip is at the correct place you pull the zip ties out and the grips will be on without waiting to dry or any thing like that.