Adding a second mobile phone number listing to the GAL without changing the schema

I have been directed to add a user's personal mobile number to the GAL.  Unfortunately there is only one slot for mobile number in the form in Active Directory users and Computers (windows 2008 version) and it is populated with her work mobile number.

I have a slot for pager but they want it to be listed as "personal mobile number"  I have already populated her home phone number as well.

Is there any way that I can add this or change "pager" to personal mobile without having to change the schema for the whole enterprise?

any variation on "personal mobile" would be acceptable as long as it is clear what it is.