It looks like cable housing to me, too. There are a few supports available though- take a look at Velo Orange`s site and see if any of their stuff will work for you. You might also be able to rest a larger bag on one of those Nashbar platforms. But unless you`re planning a custom bag of some kind, you probably won`t need anything extra since most commercially produced handlebar bags include an internal framework if they`re big enough to need one. The smaller ones just have a back plate, which is also included when you buy the bag.