Pulling in fields as view only in tickets

Pulling in fields as view only in tickets

Hi!  We have added a custom field in the Customers module (customer ID).  We want to be able to fill in customer ID from our external database and have that customer ID pull into the ticket as view only. 

Example: 
Customer Christy Smith has Customer ID 00112233 in Customers module.  When a ticket is created with Christy as the contact, we want 00112233 to be displayed in the ticket for reference.

Is this possible?  If so, how? :)