There seem to be a few folks here who suggest you figure out how to put on a good show to snooker the HD inspector and then, once his back is turned, rock and roll serving food that wasn't prepared in an HD certified kitchen.
Good luck with that, hope you have a lot of liability insurance and an LLC to protect your personal assets. Oh wait, they probably wouldn't bother with that either.
Re-heating on location is not "prepping" and cooking on location. If you cook somewhere other than where you will serve the food, that place must be HD certified; a mobile food trailer, commisary, etc.
If you want to do this, do it right per the laws and requirements of your state and county. You will find yourself much more successful in the long run. I just finished my first full year doing it legally ... IT CAN BE DONE.