quiksilver makes "board patches" for dinged surfboards...they usually come with boardshorts but if you can get your hands on those they work great for fixing stuff...dinged wakeboards, broken skin, fat sacs etc...just make sure whatever you put em on is nice and dry.
A pool supply store carries pool patch material in a big sheet with a large tube of glue. Last time I bought one it was less than $4.00 and will last for years. This will not be the last hole your patch. Just wait until a seam blows out. They are fixable as long as you have the right repair kit.
Epoxy is too stiff to patch a fat sac hole. It will not burn into the plastic either.