You can make a torch directly underneath the middle bridge block I believe.
Well I made an XNOR gate to power the bridge. The bridge is connected to two different switches, one on each side. The XNOR gate ensures the bridge will toggle on and off as you toggle either switch on and off, regardless of the position of the other switch.
If I active the bridge block with a redtone torch underneath it, the block will always be on, and it will render the XNOR gate useless.