I've just re wired my Rega again as the previous wire had damaged insulation that I didn't notice when rewiring.
I made a plug by putting a coil of waxed paper inside the mounting. I then used a pair of helping hands to hold the interconnect wire inside the mounting and then pushed epoxy repair putty inside.
This made a nice bung that fits inside the arm mount which can be secured by the grub screw. Its not the best pics but you should get the idea.
If anyone rewires a rega I can recommend this method.
The card is just holding the silicone sealant I squirted in to insulate the tonearm wires. The card will come off once it's dry.