Change User Selection List Display


I would like to tweak the following - for the service provider within the settings is the ability to use the username as the drop down or First & Last Name from their profile.

I notice that the Client (User) field is a drop down in the admin area but displays only the username, can this be modified to again display as

First Name Last name (Custom Profile Field Club or Society)

The bit in brackets I would like to use a custom profile field that I have set up called Your Club or Society.

This will allow us in the admin to easily identify the client rather than trying to remember the username of the client when adding an appointment manually in the admin area.