I think Isopropyl Alcohol is your best bet for cleaning oil off paintwork - it's quite a gentle solvent compared to petrol or white spirits and good at dissolving veg.
I've put a glyc/water mix in the pressure washer soap dispenser before, and cleaned the car with it... the paint still sees to be attached so who knows? Do remember the odd oily looking streak appear though, but it washed off just as easily.