F5 Data Guard - Expose last 4 digits for Custom Pattern

Hi, as from the screenshot below, we are able to choose to expose the last 4 digits for credit card numbers and U.S. Social Security Numbers. How about if we want to expose the last 4 digits for the custom patterns? It doesn't seem to have this option available. Anyone got idea on how to do so? 

Let's say the phone number or email address are considered as sensitive information and we don't want to mask the entire phone number and email address.