Add a piece of plywood 10" wide by the height of the door to the knob end of the door with hinges. When you need the room and privacy flip the 10" plywood out 90 degrees from the door giving you and extra wedge of room. When done fold the plywood flat against the door and close it as usual. You would have to move the stop on the door jam in 1/2" to compensate for the 1/2" plywood but it would be less work than rebuilding the wall.
A carpenter could do a nice job and make it look nice. A couple of good magnets on the 1/2" plywood and in the door jam could keep the door closed with the plywood out. Or maybe just use a hook.