I don't know if there is a way to plug it permanently but for a quick and dirty try at plugging it, I would use duct tape to roll into a plug as tight as I could make it. Then cover it with a flat piece on the inside and outside of the pot. You could always use colored paint of some sort to dab onto the surface patch to make it blend in. There is all kinds of sculpy type clay's that might work but I would be more concerned about chemicals from the plug material leaching through to the soil.
