atmasphere,
Couldn't he do the same thing at the end of the two XLR cable connectors that plugs into the preamp? Solder a jumper wire from pin 1 to pin 3 of the female connector.
I doubt he would want to void the warranty on the preamp if he did it inside the unit.
Or could he just take and old RCA interconnect cable and demo the inside pin of the plug on one end. Cut off the cable and bare the return ground wire and connect it a metal screw on the chassis. Then plug the RCA plug of the cable into any output RCA jack on the back of the preamp?
Jim