There might be some bags out there that you can attach the accessory hose to, but you have to be careful with the type of valve on the bag. Some of the bags that are designed to be pumped down by a hand-held foodsaver or by similar means utilize a “valve” that is not much more than a piece of flexible plastic that is glued to the bag. While that design is fine in the refrigerator or freezer, when exposed to heat, it could easily fail at the glue or the plastic just bends open.
If it were me, I’d just cut the shoulder in half and use two bags. Bonus is that your cook time is shorter and when you finish it in the smoker, you get more surface area which means more bark.
I’ve gone so far as to quarter a butt before smoking so that I get a higher bark to meat ratio when shredding.