you have a couple of options which would work but wouldn't be very popular and could get you banned.
1. Threaten your enemy that if he doesn't make his army withdraw you will find him once he has left mongoose hall.
2. distract your opponent once you know who you will be playing against and when no-one is looking steal their tanks and vechiles - no models, cant use 'em, therefore you win.
3. rules say wave 3 or before, therefore things like m16s are allowed, so get one, an airsoft one will do and prove that a real airsoft gun CAN destroy tanks (model ones admittably but if thats all youy opponent has don't worry) this is probably the best option, is the most fun to do and probably best to watch someone else do.
obviously none of these are good ideas but its probably better than nothing, but i've saved the best to last...
4. everyone send an email to matt asking him to change the rules so either he will correct the problem straight away or everyone bombarding him with the similar message will annoy him so much he will eventually give in and correct it.