Terrified of Stairways

Question
I have read up on dogs being afraid of stairs but my story may be a tad more complex.  I have a 2 year old Bernese Mountain Dog, raised from a pup on the ground level of a condo.  As a puppy, he has his normal initial fear of this new sight - the stairs (only one flight in the open that lead to outdoors) and he overcame it easily as any puppy would.
Now we've moved to the upper floors, and upon having an elevator break down, we head to the stairway on the side of the building, a more darker, echoey place, he will absolutely refuse to go up or down, and he will have a heart race increase, pupil dialating panting episode - utter fear strikes him.  Yes he still goes up/down the main entry way stairs.  
My concern is that in the event of a fire (elevators will remain grounded) or the elevator breaks down, I have no strength to carry him down/up these side stairs.
I've tried the "treat" method, coaxing method, for 2 weeks, 30-50 minutes a day and nothing has worked.
How can I get my 2 year old dog to overcome this fear?
It is a very big concern.  He has even bolted onto the street running from me in fear of these side stairways.

Answer
You've got the right idea, but you need to increase the reward. Make it something that he really, really likes.... like cheese or meat, etc. And don't work on the entire set of stairs at one time, but just do a couple at a time and quit, and gradually increase the number of steps. Each time you have even the smallest success, praise the heck out of him and get very excited.

This is obviously going to be a slow process, but just have patience and stick with it. Also, you might want to do this when he is hungry.