Hmm, what about a system like this? Instead of just getting the Workshop items for free, you purchase “Workshop Item” items? They’d be available in a range of different sizes (infinitesimal, small, medium, large, gigantic, etc) and be priced somewhat higher than most normal items of their size.
Each item in and of itself isn’t anything more than a box. If you edit the box, you can choose which currently subscribed Workshop item you want it to be. The item can be swapped out as desired. Each Workshop item, then, is assigned a size automatically (probably just based on volume or something simple). If the Workshop item is of the same size or smaller, then you can set the item to that Workshop item. If you want a condo full of cool Workshop things, it’ll still require a bit of grinding. This would also prevent copying of official items because it’s no longer cheaper to do so.