Requesting ability to add alts to a player's main's attendance, so that players' attendance % is consistent dependent on their participation on any character they join on, with all points gained showing next to the main character.

This is already a feature. Go to the 'Roster Editor', right-click the player's name, and select their alt one at a time. Once that's done, it looks like this on your main window:

Edit: Unless you're talking about just combining them all into one row as opposed to having to show alts in the window.