[JBird]

The only answer I can come up with is to just have specific penalties applied to each unnatural size that would be fitting to how they work against the character. For example: if the breasts are, say, as large as the entire torso, then the character would have trouble maneuvering and dodging, regardless of support (unless, of course, high strength involved, somehow). I've played a few DnD games among friends, and there have been times where, based on how unsuccessful the roll, heavy weapons end up working against the player.

If the character needs a breast cart, then I can't really see how she would be useful in battle. But, then again, I haven't played a BE-infused game.