I reamed a hole that went behind the servo and routed the servo wire in through the battery tunnel. To help ensure the battery wouldn't pinch the servo wires I used a cut-off wheel to dremel a channel for the servo wire to go along the inside of the battery tunnel.

Other than that I just use an X-acto blade to apply just the tiniest little specs of CA onto the chassis to hold down the wire. It's just enough to hold it down but can still be easily pulled up if needed .