When I was fuel-proofing my fire wall I did the same thing - got epoxy inside the blind nuts. All you need to do is make a run to your local hardware store, or maybe even you local hobby shop, and pick-up a tap and drill set. They're about $3. I would bring a motor mount bolt with you to get the correct size. Keep in mind that most of the hardware in ARFs are metric. In my particular case the bolts were 4mm. Then just drill out the epoxy with an undersized bit, taking care not to damage the blind nuts, and run the tap through. Everything should be good after that. Good luck.