There are no guarentees with block paving as it can soak up a lot of oil if it has not been sealed and if the oil was dirty then its almost impossible to get the stains out. However the first thing to do is draw up as much up the oil as possible and ( we have never done this ) it is said that Talcum Powder or flour will draw some up. Its then just an elbow grease job of hands and knees scrubbing with a detergent and then warm, soapy water.
There are various agents which mechanics use to clean engines and you could try these but, as with every experiment, there can be side effects so try it out on a small area behind a bush or somewhere hidden.
I have been told that WD40 is good for removing oil, a bricklayer that lays block paving told me this. Would of been the last thing I would of tried, but ill give it a go. Just thought i'd tell you incase someone else has the same problem.
He said it is slow and needs to be applied everyday but will eventually totally remove the oil stains.