Hey Rob,
You could uncouple the actuator. Sorry, I don't have an A/C box that I could take a picture of, but there is a clip that couples the actuator arm to the door. It is on the front side so I don't think you need to drop the box. Getting to it may be a PITA. Once uncoupled, I guess you could use some wire to hold the door pointing for the defrosters.
Slotts