I recently fitted a set of Ariette grips identical to the OE ones (part no. HAA58397 from Motorworks, £23.18 incl VAT P&P for two sets) to replace the worn ones. You will need two sets as both sides require the extra internal diameter of the throttle grip (I have two spare clutch side, non-heated grips if anyone wants them!).
The old grips are held by two small blobs of "stick", one on the inboard end nearest the switchgear and one at the bar-end weight end. I replaced the new ones using the wifes hairspray liberally, no glue, which has worked perfectly. As you start to peel the old grips off, use a stanley type knife to cut the grip down its length avoiding cutting through to the heated part. Total job took 30 minutes.
See the thread below for photographic assistance, but cut both grips off as per Mike O's second grip for ease.
Managed to remove the o/e rubber grips without damaging the heating elements and replaced them with Baja foam grips, noticable differnce in comfort for motorway cruising...NO VIBES