Reverse audio jack for front and back speakers
How about something like this?







simulate this circuit &ndash; Schematic created using CircuitLab

Tie all the grounds together and flipping both switches will swap the speakers. The switches are DPDT. Keep all the wires short and you shouldn't introduce too much noise. You could do it all with one switch if you use a 4PDT, like this one.

Note that the Left Right channels are not flipped by this switch, that's already done in software if your computer is expecting the speakers to be behind the person, like it is for surround sound channels.