I went ahead and changed this thread type from a Question to an Idea, as this is not current functionality in SmarterTrack. I do think it's a great idea though!
You wouldn't be able to send them the ticket link you find when you popout a ticket in its own window, as an end user won't have access to the Management Interface. However, having a way to append a message to your replies that links to your support portal's Tickets section would be beneficial. Or even adding a way to directly link to their ticket in the portal.
A possible workaround for the time being may be to use System Events to follow up with another reply when ticket messages are sent, and that reply could include a link to your portal. It's not an ideal solution, I know, but it's something...