Lists: Filter by "hidden" fields

As a dispatcher and strategist, a user has created custom fields and stores data in those fields, but has them hidden from the user interface. The user would like to be able to filter contacts or groups lists by these hidden custom fields.

*Note: Disciple.Tools hides many of WordPress' default fields as well and a simple filtering of all hidden fields would double the list of filter options and make it unmanageable. We will need to find a solution that allows the adding of select hidden fields to the list of filters available for filtering records.