We play it with the tower board off to the side of the main board. When a player enters the crown space on the main board they move to the first space in the tower and continue from there.
We wanted to play it this way too, but it seems a little weird doing it, since if you are able to get past the mines/crypt, you will probibly be able to just breeze through the tower. We are planning to play it that way this weekend though, to give it a try.
Thanks to everyone else for their responses.