Russ,

Sorry to hear about your accident but you can lower the cock to the half cock possition while the lock is outside its mortice. Grasp the lock plate firmly in your left hand keeping body part away from where the cock would fall should it slip. Wrap the right hand thumb over the cock between the upper jaw and the screw, then with the middle finger gently push up on the sear bar while pulling back with your thumb. Gently lower the cock into the half cock notch or even into the full down possition once you feel the mainspring take over. If you lock has a fly you will need to lower the hamer past the half-cock notch to clear the fly and then pull back to lock it in. If you lock does not have a fly you can simple lower the lock into the half cock notch.

I do this a lot when re-assembling a lock after polishing, borwning, and inletting into a new stock.