It's good to see somebody that is thinking outside of the box.
I tried this a while back with not so good results. I actually lost one of the banks.
Anyway, you need a SPDT switch similar to the ones used for the multiple hard drive mods.
You have to remove the top half of the switch on the chip, the part that actually slides.
Once you get that removed, you can see how the switch works and how the switch is soldered in.
The use 30 gauage solid core wire and solder to each of the six pads on the switch.
Then just match the wiring to your new external switch.
It will work, I just used to heavy a wire. I think it was 22 gauge. I lifted three ofthe pads and destroyed two traces.
The switch did work before this happened though
Good Luck
Megahurt