Here's another vote for either using a Palmer's male stab as your foregrip (replace the expansion chamber with this), or using a female stab as your bottomline ASA. Palmer's stabs are high quality and can handle CO2 as you know, and they're very consistent. Tippmann guys (98's, A5's and X7C's) have been using them for years and have always recommended them.
If it were me, I'd use a male stab to replace the expansion chamber because, if the stab is working, then there's no liquid CO2 getting output in the first place. Then I'd still replace the bottomline ASA with a nice venting, on/off ASA like a CP direct mount, Hybrid, or POPS.
And, as mentioned, after your regulator/stab is in place, do the mod to eliminate the FVA
and set your velocity by using just the stab.