I have been having a close look at mine today, i can see a couple of mounting points one on the front of the inner engine bay and one on the inner wing that a metal bar / plate could go across to prevent the headlamp wires from being unplugged , i will get a soft steel strap to get the shape right then will get something stronger made.
Something else i considered whilst under the bonnet is removing a relay i will be looking at diagrams to see which one would stop the car starting or being used.