There may be an easier way, but this is how I was able to get the 12 digit disney confirmation number. You need to call orbitz and ask to speak to a hotel specialist. Ask them to place you on hold and call disney to make some kind of request. I have two rooms booked with them at POR so I said that I wanted to request connecting rooms. I suppose you could say you want first floor or any type of request. The hotel specialist will eventually (I think I held for a good five minutes) come back on and give the Disney won't guarantee it but will try, yada, yada, yada speech. At that point they will have that Disney number. They will give it to you. My orbitz person could not see the disney number until after they spoke with POR.
They will try to give 6 letters and other various things, but it needs to be 12 numbers.
Hope this helps!