Hey Sally,
Thanks for reaching out.
Adding a custom filter like this is technically possible, but not without some extensive custom coding far outside the scope of support. 🙁 You can learn more about that here.
So to implement the features you describe, you would have to write that custom code or hire a professional developer to do it for you. We have a list of great developers here → http://m.tri.be/18k1 (and have no affiliation with any of these folks—they’re simply some well-respected names in the community that we’ve compiled to share in situations like this one).
Sorry to disappoint! Please let me know if there are any other issues or questions I can try to help with.
Sincerely,
George