You aren't going to get any output from the login trigger.
Understanding login trigger output
I don't think this is a requirement you can meet by just implementing something on the server side. Each client will have to be modified to request the previous login data from the server and display it to the user.
You can use a login trigger to maintain a history of login times for each uid, the client would then select the most recent login time from that history for their own uid that was older than the sysprocesses.loggedindatetime value for their own spid.
-bret