How about some foam pipe insulation, then wrap it in duct tape? Cheap and easy, but kinda ugly even when done well. I think plastic tubing would also be a good idea, but I would definately weld the seam you'll have to cut to get it on. I've seen aftermarket handles like this, but am having trouble remembering where...
"A witty saying proves nothing."
- Voltaire (1694-1778)