How about that powdered oil remover you can buy for cement garage floors? My husbandf has used it in the past for car oil stains and it does a pretty good job. I don't know the name, but most big box building supply or auto shops carry it.

I work for an asphalt paving company (driveways, parking lots, etc.). We have had customers that have gotten car oil on their driveways and we tell them to sprinkle powder Tide on the area and let it set over night, then take a scrub brush and the water hose to it the next day. It may take a couple of times, but it normally works. It may be worth a shot. Good luck.