Our old trade method was to use a long thin screwdriver. Insert the flat blade through the end hole and carefully push it along between the rubber and bar. Then turn the screwdriver as if on a screw and it will wind around the bar, breaking the seal. If you can squirt a tiny drop of water in, that will help. Then the rubber should twist off.
To refit it, smear a little rubber solution from your puncture outfit into the start of the dry grip, then slide it on all the way in one quick action, avoiding it sticking half way. Then leave for a while and it will set firmly in place.