If it has been in that position very long it may be stuck. Sometimes they are very hard to get back in the right place.
Try getting the front system sealed up, then break the rear loss or open a bleeder on the rear, and push the pedal, this should kick the switch back the other way. You may have to gravity bleed to get fluid back in the front system ( or use a pressure bleeder ) until you do get some fluid in the front, the switch will probably just kick back and forth. Sometimes they go easy and sometimes they don't. If you can find one there is a special tool that screws into the valve to lock it in the center for bleeding purposes. There should be a brake warning light on the dash telling you that pressure has failed at one end or the other, and that the switch has moved. When the light dosn't come on when the pedal is pushed with the key on, then the switch is in the neutral position. Brakes should be bleed starting with the furthest away bleeder, RR then LR then RF then LF. You may have to replace the switch to get the system bleed.
I'll try this picture of the tool, I can't get a clear shot for some reason.