DPDT Switch has pins arranged like this:
1 3 5
2 4 6
positive from power input to lug 3, negative to lug 4. wire the positive input of the lamp to lug 1, wire the negative input of the lamp to lug 2. As long as you don't mix the positive and negative up you're golden.
It would work just as well with lug 5 and 6 to the lamp. It doesn't matter that the other side of the switch isn't connected - if there's not a complete circuit then there's nowhere for the electrickery to go, so it won't go anywhere.
Be aware though that wiring lamps on the same ring as audio stuff could introduce noise to your bass rig...