I was wondering this and I tried to do it with a custom lobby but was unsuccesful. Anyone know if this would be possible?

I think there is a hard limit on the max amount of vehicles on a map. Don't quote me, I'm trying to remember an obscure reply that an EA community manager mentioned. But apparently vehicles add a huge load on the game compared to other units, so latency and rendering are impacted severely when there are too many vehicles.