He can get the external power source for them, saves an additional rout. I bought a battery box to house the battery in my EXA-1 kit, but the EXA has some nice square edges to rout in to, not sure it would be feasible with the mockingbird style body.
The route has been done, in a spot next to the control cavity, and away from bridge posts. Once the batter box arrives it should slot in neatly, overlapping the route edges.