So Q&A 312 refers to a cylinder plugged at both ends. You cannot vent it with the pressure release valve so that is not legal. The Q&A does not address directly plumbing the cylinder to the working pressure line.
Unless there is a rule stating cylinders must be plumbed through a control valve, I don't see how it could not be legal. (Q&A unless Q&A rules otherwise) The pressure regulator is self relieving by rule so over pressurizing the system is not an issue. Now if you where to add a couple of check valves & turned it into a air pump... But check valves are not allowed by rule. Nevermind.
On the subject of bumpers. For this year only you can put lead-iron rods in your pool noodles?
