Unless I’m missing something, this doesn’t exist yet. We can only use the values of a picklist or reference field for a multiselect filter. It would be nice to be able to specify those manually.
Yes it would be nice. Consider this at least under consideration. It may not be feasible though. Multiselects are birds of a different feather.
I just found this post. I second Matt’s idea! I could see how it might not be feasible, but… it would be cool!