Welcome to the boards, Melb_Wiz! May you happily flush all the annoying problems in the Gael Serran...
You've already got excellent suggestions from two of our regulars. Now, let one of the irregulars add one more thought
I do believe that somewhere in the Best Tips thread is also a reference to trying to walk up that passageway backward; that somehow, that will let you sneak through. You might try that, but as Radek said, all you get up there are the answers.
Keep us posted on how you're going! We welcome fresh mea- ah, I mean new members to the boards