For a PFS character, faction is mandatory. It's at the top of the example character sheet (see PFS Guide).
If the top details on the output sheets followed the description checks so that items not checked did not appear and custom items added did appear, then it would be possible to add a custom "Faction" item and it would appear in the top details. You may need to make a few items mandatory.
Not an ideal solution as it would require the user to enter the faction in two places, but it does get it at the top of the sheet.