There's an interesting product you can buy under Accessories at the Pro Shop; the Virtual Golf Bag. It's aesthetically pleasing and sits next to you as you tee off!
Now if you can have a virtual golf bag sitting there it's not a stretch to imagine purchasing a caddie. Of course you'd only see them from the back and they'd probably just be standing there with their arms folded or hands in their pockets but I'm sure that as a virtual product it would be wildly popular among players and almost everyone would want to buy one.
It could be introduced and bought under the avatar section and clearly labeled as a caddie in the description with various avatars available at a range of CR costs.
No doubt there would be some requests to introduce certain types of caddie (Angelo Argea, Eddie Lowery, Fanny Sunesson, Steve Williams and Oddjob spring to mind) but the creative choices and development rests with WGT.
The marketing/business decision to introduce caddies however is one I strongly recommend WGT capitalize on.