Too sad that WinPopup windows do not seem to allow cut&paste.
Otherwise you could use a small web page where people can register
their netbios name or PC logon or IP address for notification and
then get pop up windows by smbclient -M that give them a URL to
visit for details.

On a second thought, you might still figure out a scheme where
each registered client gets a unique URL (maybe with his or her
netbios name, PC logon or IP address or somesuch in the URL or
in a -shudder- cookie) and use the smbclient -M popup window
only for telling them "please revisit your bookmarked page".