[bsftcs]

The character wearing the dragon armour must be the active character. Even with him or her active your party will still be pushed back a bit by the wall but you must try to walk on. (Try stepping from side to side). Later on you will have to swim upstream which can seem just as difficult. You should then be able to reach the switch.

If that still does not work you can still "vanish" past the firebeast. Stand in the corridor just before you get to the bronze firebeast and cast the vanish spell. After a few attempts you should be able to turn up just by the switch.