Haven't tried combining them myself, but, I've heard AMEX will do it for you under certain conditions. For me it's been simple to deal with the remaining small balances since I got a bunch of the photo gift cards with various photo's of the 'little hawks' on them. Once they're down to a small balance, I just give them to family members for birthdays, Christmas and other such gifts. The small denomination GC's with photos on them given out last Christmas were a big hit.

Otherwise, I still think you can just ask whatever store you're at to run the cost up to the remaining value of the GC, then pay off the rest with another GC or CC.