Custom field regular expression or blank

-- HikaShop version -- : 3.2.1
-- Joomla version -- : 3.8.2
-- PHP version -- : 7.0

I believe I am correct in saying that the regular expression check is not performed unless the custom field is set to Required.

The problem is that we want to do both..have optional fields, but make sure that they are formatted properly or left blank.

I have as an example the regular expression: (^\D?(\d{3})\D?\D?(\d{3})\D?(\d{4})$)|^$

This will validate a properly formatted number (for US) or blank. But we can't get past the restrictions of the default behavior. We need either a properly formatted input, or nothing at all.

Is this possible with a work-around?

***EDIT: I just found conditional field options...so I created an input for SMS Notifications and then made the mobile number with the regex conditional on that...so its a temporary work around. It would be cool though to be able to format input on optional fields ***

Thank you!