I would guess that some heat from a propane torch might help. the good epoxy is some tough stuff. Always use marine tex OR Devcon for metal (they make some for plastic too) try to find a small tip for the propane torch or use one of those small butane torches (like they sell at Harbor Freight, the orange ones). Other than that I cannot think of anything that would dissolve the hardened epoxy (acetone, anybody know if acetone would dissolve epoxy?). Being that the 2 wells are so close together, you may end up doing both over again. (once you heat up one the other probably will be affected).