Step 1: What You Need
Step 2: Make the Mold
Mold the Sugru into a shape the length of the RCA connector. Smash the RCA connector into the Sugru as shown.
Step 3: Add the Wires
Add the positive(red) and ground(black) wires as shown. connect the other ends to your circuit or adapter etc.
It works great and after it's set it's reusable.
Did this at Arch Reactor Hackerspace Sugru hack something night. :-)