Hi James,
Great question!
Might it be viable for you to use categories or tags for this purpose?
If not you might need to consider a custom filter implementation: thankfully, Filter Bar has been built in a way that facilitates all kinds of customizations including the addition of completely new filters, so doing so is readily achievable.
That said, such a customization is something we’d really need to leave in your hands (if you find categories and tags are unsuitable for the task) and you would definitely need a fairly good grounding in WordPress development to drive it forward.
I hope that helps!