Rob, this has been on our Roadmap for a while and has been taking longer than expected. On the roadmap we have a feature called “Multi Value Dropdown” which is essentially exactly what you’re looking for.
This is a mockup, but it’ll be something like this:
I would estimate we’ll have this around mid to late August.
We’re now finalizing the search component and will have that published by Sat night. (7/11)