is it possible to dynamically change whether a button is visible or not during run-time.

i need something similar to this:
http://www.coniserver.net/ubbthreads/showflat.php/Cat/0/Number/770585/an/0/page/0#Post770585

I have a panel that displays buttons (names) of previously visited locations. the player can bring up the menu and select the location and teleport there, but only places that he has already visited. I don't want the player to see places that he has NOT already visited.

i am having problems programming this. The manual says i can use the dot modifier, but not to access the indivisual buttons.

Can someone help me? Any suggestions would be appreciated or perhaps maybe there is a different method?