Adding a field to the Simple Search Panel - Personalization

Hello, 

Is it possible to add the External Reference value to the Simple Search Panel. We would like to be able to use the Simple Search to search on the External Reference field, but I cannot figure out how to do this. 

Is it possible and if so, can someone provide the steps for doing this.

This is a searchable field in the Advanced Search, so I would expect it to be available for Personalization to add to the Simple Search. So far I have been able to add it to the Search Results (Table) and I have changed the Prompt.