Looks like a Gregoire slip on grip. I was able to remove mine from my Tiger's yoke this summer when it was near 100F by simply wiggling it and pulling it off. I figure that I will warm it with a hair dryer or heat gun if I have to remove it again when the weather is cooler.
I think Tim's suggestion of compressed air makes sense, but I would combine it with warming the rubber first. The issue I see with that working is that, if yours is like mine, the PTT wire runs down the side of the yoke between the inside of the grip and the yoke handle. Much of the compressed air will leak out along the space made by the wire, so you will need enough air volume to overcome that and still pressurize under the grip.
On mine there was a fair amount of wire slack coiled in the space between the end of the grip and the top of the yoke handle. The PTT switch could actually be pulled out of the grip from the outside to access its solder joints. If yours is similar, you might be able to reach down through the hole with a tweezer and pull the switch upwards until enough protrudes out of the grip that you can grab it with a pair of needle nose pliers and pull it back into position.