Like Seabronc said, you're real issue won't be the switch. It will be the power supply. Unless you're going to keep a battery in the back, you'll have to rewire the circuit anyway to get power, and will probably end up fixing it anyway. Why put the effort to rig it up, when you could fix it with not much more effort?
There's a lot of ways you could rig it to get to t from the inside depending on your problem. If it's just a power issue, you could keep a battery in the back and wire it to that, but if it's the switch you may as well fix one of the two switches. It may cost a tad more to get the right switch, but it will be worth it when you consider the extra time and effort making your own would entail.
brad