This approach might work:
Create a table for listing user, account names or both. (It depends on how you've set things up to determine which work for you.)
Create a script that preforms when the file is opened that:
Creates a record in the table and stores their user and/or account names. (get(UserName) and Get(AccountName)).
Display this table in a portal and you've got your logged in list.
Create another script to remove the user's log in record from the table and set it to perform when the file is closed.
Funny seeing you here, again... ;-)
I'll give this a try and let you know my results!