I'm a detergent chemist. Most detergents are derived from petroleum, so does that count? Anyways, in reading your message my first thought was the iron and a cloth approach, but with a polyester rag which will have more affinity for the oil (ever try to get an oil stain out of polyester?). Another approach would be to use a generous amount of solvent like Coleman lantern fuel and simply try to wash the stain out. I have used used this stuff on wood before to remove adhesive and it does not leave any stains. One caution would be to do this outside and away from the iron or anything that could ignite the fuel. If you go the solvent route, you might want to test it on some scrap to make sure it does not spread the stain and make the scar bigger.

As far as fiberglassing, I would not think that a little oil contaimnation would hurt the bond. Plenty of boats have been made from air-dried sappy woods like spruce and pine and oily woods like teak and then fiberglassed without a problem. Best of success.