EDIT: Here's a random thought on the M20; give it an innate button ability. Would really help the guys trying to shoot down a rushed Puma with bazookas. Would also really give Axis players a second thought into trying to rush their Panzer4 against your AT gun or Jackson. It'll cost munitions and also could be a vet1 ability, so if you're desperate for a good AT support you can try the veteran vehicle switcheroo.
I totally can't see this working out too well.
1. It is an ability that requires a unit to stand still, and that is likely suicidal for a light vehicle to hope to maintain. It is currently already a difficult and unlikely ability to pull off for long on Guards - I'd only imagine starting it would be easier on M20s, but making it last any appreciable time would be nigh impossible in any remotely large battle.
1. A few machine-gunners and riflemen pinning down a tank is already sorta silly, but one machine-gunner on a vehicle would be the height of silliness.