XF 1.5 Admin Notes for Users Awaiting Approval

Here's the problem: Our board requires approval by Admins to determine if application meets certain criteria. Occasionally we want to let other admins know that we're communicating with an applicant so another doesn't inadvertently approve the application prematurely.

I thought about creating a custom user field called "Admin Notes" but custom user fields are visible by the user.

Is there any method to create an admin only note for the purposes I described?