Ok this has just been done and found by my self.
You can open the boss room door to the 4th boss without even killing the third boss. This is very good for a group who are having issues with the this boss. This will also let the group complete hard mode so they can all get more medallion.
Make sure you have a burglar in your group.
- Start fighting the third boss in SG.
In the 3rd stage of the fight(Blue ghosts - Do not kill any of them) all die.
Burg use hips a the gate.
The gate will open and boss will reset and the door to the 4th Hard more boss will open
The boss room is now open you do not even have to kill the third boss!
This is 100% working as i have tested this 3 times and it worked 3 times!
Enjoy!