Air worked with mine, but at first you may find some grip glue holding it on. As a last resort, you can push something very small in to loosen it, like a jeweller's screwdriver or thin blade, and maybe only part way in will get you started. The idea is not to distort it too much so you don't break the heating wires buried in the rubber. The soap idea might work, but if you blow air and twist clockwise against the throttle stop, with a little patience it should break the glue and come off. I wouldn't recommend any solvents or WD40 as they may degrade the grip long term. When you reinstall, a thin line of RTV gasket maker will be sufficient to hold it in place, and be sure to align the power wire appropriately. Use air again to assist getting it back on.
