kerosene or something like "goof off" or "oops" might work. Never had a dog with sap on it before though, so its just a suggestion, like anything else I would try it on a small spot first to see if the animal has a reaction. And make sure you use it in a well vented area. I would think as long as you put it on a rag first then work it into the hair it shouldn't bother the animal, but again test on a small area first.

Shadow out !!!