It's been a long time since I hiked through that area, so I don't know about that requirement, which must be new. If they're requiring a bear canister (which I use all the time when backpacking in the Sierra), then I don't know if they'd allow an Ursack as an alternative... but that is one potential option. I would still hang an Ursack though, using proper bear bagging technique.
Now that I've gotten used to carrying a bear can (plastic) in the Sierra, I personally wouldn't mind carrying one on the A.T. or anywhere else that has a lot of bear activity. It would definitely keep the little critters out of the food as well. Yes, it adds weight compared to an Ursack or stuff sack, but it is better for critter-proofing if used correctly. I put anything with an odor (ie. toothpaste) in there at night.
That said, an Ursack would be my recommendation for another option if permitted in the area.