In reply to Shearwater:
I was thinking similarly to Toby - my old Macpac just has compression straps on the side, which don't have a releasable buckle on, but it's possible to slide skis into from the top and set up an A-carry. I think the new ones may have standard releasable buckles, though - I had a look a year or two back, although was probably looking at slightly smaller sacs.
But it is worth checking they're actually long enough to get the binding through to the level you need it reasonably easily, particularly once rucsac is fully packed. Can be a tight squeeze with touring bindings, and on at least one of my sacs it's just that bit too short, so seems fine in the shop, or even when first setting off from the car, but too much faff once you have cold hands, gloves on, and everything's covered in a layer of snow.