I used 'flexible' epoxy, used in repairing composite car bumpers. I started by 'opening up' the cracks with a sharp blade (some of them up to a quarter of an inch). This will allow the material to sit nice and deep.
After drying, the blade can be used to 'shave' the epoxy till it's level, then use 220 grit paper followed by a 400 water sanding. A nice coat of primer-filler followed by a few coats of lacquer in the color of your choice. Voila!
The cracks WILL eventually come back:( . The integrity of the original 'molded' steering wheel has been irreversably affected, but they will show up as hairline cracks.
Hope this helps?
whizzerick
