Please post back and let us know if the combination of numerous cards into one works. I tried the same thing at the store in NYC and was told no, I had to call.
I called the guest services number and was once again told no it was not possible, only in WDW. I even called the number on the back of the gift cards. I would rather have all the money on one card. It is a nice way to save for a trip, but a pain when trying to make the final transactions.