Short of being able to sync with other officers
Guild Organizer can do this. You just put the name of the main for each alt a person has in their officer notes and hit the combine button. When they are on their main the name appears as normal. When on an alt they are highlighted amd have their mains name in brackets.
Can also view all alts a main has by clicking the little + next to a name. Its not been updated for the current patch but mines been working just fine. Only issue im aware of if alpha map seems to break it and show a blank window.
Give it a try =)