Prevent Duplicates across multiple User View Settings Fields

I am building a board view where I would like to be able to select a single user from the list of selected users in the Board View Settings Field. I could accomplish this in the app itself, but it would be a smoother experience if this could be done from the settings pane. These are a couple hypothetical solutions, but I have not found a way to implement them.

1. Add a “dropdown” settings field and populate it with the values in my “user” settings field
2. Add a second “user” settings field and somehow limit it to one user and prevent duplicates. (AKA, Is there a way to populate the options for one setting field with the results of another?)
3. Build the experience in the board view itself

If anyone has done something similar, I would really appreciate some guidance!