Maybe with additional comrades, so there is only 2 Operator PCs each with 2 comrades (again vehicle dependent). One can pick tank ace at the first milestone to mix it up a bit (the fact that you keep comrade advances is awesome for this). The rest of the squad can be infantry supporting the tank.
Gives the players variety in classes, but still would require a large player group to seem realistic (A lone Leman Russ with a Segeant and Vox Tech running around behind it would look pretty weird).
Ultimately, Vehicles with crews greater than 2 (or lesser, what does a sentinel operators comrade do?) are poorly implemented in Only War and so are the concepts for armored regiments. Armored regiments have a completely different structure to infantry, on that in game terms would require a completely different set of classes, or at least variants of the current choices.