All the pneumatic companies make spun stainless steel air-reservoirs. But for trials variable volume would be good. Like the pneumatic cylinder and lock it at different lengths.
I would just T it inline near the bag and let the short length of small diameter line provide some extra damping.
Right now I've got to chop my spare EAS kicker cable into a EAS unlock-suite cable and see why my one hangs to the left at std ride height. I wonder if that section of the height sensors are worn out?

