Im thinking this is going to be a simple one for someone but I just cant see it.

In the assignee box in the ticketing page when customers click the dropdown box it gives them a list of Users some of these users are my customers (Business owners that I have created accounts for) as opposed to support staff.

Is there a way to create people as users but not have them show up in the assignee box.

 

I created a User role called Support Customers, I have all customers under there own orginisations & Machines are in Groups Specific to each client.