This could easily be done, its quite simple, use this code:

on *:LOGON:*:{
; CAP request for "away-notify" - This is required for this script to fully work!
raw CAP LS
raw CAP REQ :away-notify
raw CAP END
}
raw AWAY:*: {
if ($1) { echo -a $network 8,1AWAY:9,1 $nick 7,1is Away:11,1 $strip($1-) | halt }
if (!$1) { echo -a $network 8,1AWAY:9,1 $nick 7,1is Back! | halt }
}

This will output to the current window who goes away on what network, including the users reason.

In the current active window, it will show one of the following replies:
eg. AWAY -> Network AWAY: username is Away: away reason
eg. BACK -> Network AWAY: username is Back!

This script only shows in the active window who marks themselves as away, but it could be adjusted to mark the user list names if edited.

I do not know how to edit the user list in the client, not even sure you could, unless you scripted a full user list then applied this script to it.