Drill out the interior wall panel rivets below, or above, the windows. The interior panel can be moved away from the formers ....enough to put in new wiring. You have to make holes, and rubber grommet them, thru the formers as you run the wire. Then re-rivet (or screw) the interior panel back in place. This not the correct way, which is to completely remove the panels and run the wires. But it will work for you.
"If it can't be reduced, reused, repaired, rebuilt, refurbished, refinished, resold, recycled or composted
then it should be restricted, redesigned or removed from production."