It's "not a thing" because there would be nothing to do with the thing. Glamours need a base item to attach to, and there is no separate item for the aetherotransformer. It can't be applied to the gun or there would be no information about which gun you have glamoured.

If they were going to add more toggles to character appearance choices (which they don't or can't do in general), they would likely be spent on something more universal than a choice that only affects one or two classes.

So the only way might be to split the weapon to have a separate off-hand element, which might have implications for IL or inventory.