As lubricants go WD40 is pretty light. If there isn't too much on the pads you might get lucky and be able to dissolve it out with solvent. It's worth a try at least. Sometimes even mud or water can sort out small amounts of contamination.
I wouldn't recommend burning it off if you don't know what you are doing. Too much heat can weaken the bond between the pad and backing plate causing them to separate during use.