Not that exact scenario...I did do this that you may find helpful...
I took a set of Garrett black phones that came with my At Pro an cut off that G Pro proprietary plug, soldered on a common 90 degree 1/4" jack so I could use those G phones a different mfgs rig.....If I remember, theres only 3 wires...black, white, and red..it was pretty easy...so I could assume you could wire in an On/Off switch equally as easy....best thing to do is simply twist the wires together, fire up your rig, and determine which wires you will need to go through the switch to give you your desired results....sort of a 'process of elimination' kind of deal....should only take you 10 minutes to figure it out all on your own...report back though for the groups knowledge...
Mud