Oh. For that, use several mounted images, maybe.
- Right Hand Weapon
- Left Hand Weapon
- Armour
- Holstered weapon A
- Holstered weapon B
...
Split it up into more than one model. Look at TwoGuns for an example of this - the Pistol, Akimbo Pistol, Holstered Pistol and Holstered Akimbo Pistol are each separate shapeBaseImageData datablocks, along with shared particle effects and an item with a few fields.