User field: can I limit choices to users of a specific Role?

Is there any way to have the users shown in a user field limited to users of a specific role?

Use case:

The app has a role called "approvers"

In a form, I want a "Select Approver" field that would be a "user" type field. The selected user would get a notification.

I know I can make a "custom user set", but every time an approver needs to be added or removed, an admin would have to go in and edit the field. This information is already in the app per the role. It would be much better to simply have a field that allows you to select from this list of users with the approver role. 

Is there any way to accomplish this?

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Paul Easton
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