This may be only peripherally helpful in this case, but most kitty litters are made of dried clay, and so are the oil-dry products used in auto shops to absorb oil spills. Might help with the rest of the mess from the incident.

The solvents that readily dissolve motor oil (such as spray carburetor cleaner, spray brake parts cleaner, and gasoline) would likely cause more problems than they solve. You certainly wouldn't want the cat to ingest them, and they'd almost certainly irritate his (her?) skin a lot. Creme-style hand cleaner (one brand is "Goop") might be less dangerous, but it would be a logistical nightmare to apply and rub in thoroughly, and it would still have to be rinsed.

A drying/absorbing agent such as those previously suggested, followed by a warm soapy bath (use lots of soap) and a warm water rinse is probably the best bet.