the end cap doesn't twist on its just pressed on. its hard to get off with out taking the rubber off tho. take a razor and cut down the rubber and peal it off like a banana the cap will come off with it
Just wanted to piggyback on this thread that this method works really well, and my stock grips are in perfect shape afterwards.
Also to note...the throttle grip end screws counter-clockwise off, and then you can easily work the clothes hanger under the rubber and perform the removal technique in the link. For the clutch side grip, the grip end is held on to the rubber of the grip by two small clips on either side; just work between the end and the rubber of the grip till you separate the two...then remove the grip the same as the throttle side.
BTW...thanks for the post to this link, it was really helpful!