Crude but effective diagram....
Pos. Terminal retainer is just a thin section if copper pipe. Cut a piece out of it so it fits snugly inside the tube. Position it where you like, and sweat solder it in place.
The isolator will now rest against this allowing ample room above it for wiring and switch.
I made the isolator out of an old junk screwdriver handle. Ground it down to the correct circumfrence to fit in the tube, then lopped of a section with a hack saw. Insert brass screw in the center, and your done.