Could a hybridization of the 2 methods listed above be successful?
Say you used a piece of high pressure seamless schedule 80 steel pipe (12" diameter or under
to maintain a safe working pressure of 1800psi or more) that you packed part way (1/3-1/2)
full of trim (on top of a screen maybe) then topped with equal-double that volume in dry ice before capping and bringing to a pressure over 1100psi (using a nitrox/scuba tank and high pressure regulator). Then warm it up to/maintain a temperature over 90F (maybe using a water jacket and the heating element/thermostat from a hot water heater, they commonly go up to 125F or wrap in a couple/few hundred watts worth of heating tape and use a router control as a manual thermostat) I assume you might want to give it a while to steep, then slowly bleed off from the bottom of your steel pipe pressure vessel via a high pressure valve (while maintaining nitrox pressure and temp) Capture what comes out (maybe in a series of cascading "capture vessels" made out of 5 gallon buckets and PVC pipe or something)
It would be Kindof like an espresso machine
I bet there are some paintball enthusiasts out there that could fabricate an experimental/test version in relatively short time using many things they might already have on hand... Maybe a bulk fill/remote tank adapter and Nitrox tank with 1200 psi regulator (you could probably inline the whole thing using high pressure fittings).
Though the burst pressure of the pipe mentioned above is 6500psi or better (more than the
working pressure of a nitrox tank) I would still probably make provisions for a CO2 burst
disk (commonly 2500-3000psi I think) safety valve in the lid of your steel pipe pressure
vessel just in case things go wrong. (if the thing catastrophically failed while you are near
by I have a feeling it would at least cost you your hearing).
If everything is done right (using the appropriate pressure rated parts and procedure) the
steel pipe pressure vessel should actually be tougher than the aluminum liquid co2 tanks
commonly used and abused by paintballers..
It would actually be quite similar to the hybrid rocket made on that mythbusters TV show,
though operate at around 50% higher pressures.. Not much of a stretch really, I'm fairly sure they engineered in some broad margins for safety and I'm pretty sure they were still using sch 40 pipe. If kept to 8" diameter or under (seamless high pressure pipe) you could too while maintaining a 4500psi or higher burst pressure, still quite a bit higher than your safety burst disks.
8" pipe 4' long would have the (1/2 full, lightly packed) capacity of about a 5 gallon bucket..
A 6 incher the same length would hold about 3 gallons, that's still more than you could run through a bubble bag in a single pass (and it would have a working pressure rating exactly on par wit what we are doing)..
A 4 inch pipe (4 foot long) would hold about half that of a 6" and is probably more on par with what you would regularly be passing through your 5 gallon bubble bags.. It would also be overbuilt having a burst pressure over 6000psi (9k if you used sch 80, 14k for sch 160)..
Hell technically speaking Standard Wrought Steel sch 40 4" steel pipe (from the hardware store) has a burst pressure over 5000psi, being more than 4 times your working pressure it could be considered safe (I'd mark the seem and keep it pointed in the safest possible direction while under pressure, also mike the middle of the pipe directly over the seem before and after every usage and stop using it if things start to deform).
You could build it in an afternoon only having to stop at the paintball guy, hardware store. and wherever you get your dry ice. You could probably do it for under $500. (half that if you buy your nitrox tank and remote kit used) don't forget the extra CO2 burst disk and shutoff valve too (where the remote kit hose meets the gun adapter?) Tell the guy that's what it takes to make the deal happen and he'll probably throw it all in for free, otherwise offer him an extra $20. (The cheap stuff on ebay doesn't sell for much more).. Oh yeah, make sure any tank you buy is "in hydro" (means its up on its pressure testing) otherwise you can't get it filled..
You know if you used the remote kit the way it was designed to be (instead of taking it apart) you could probably make the thing 2 foot longer (increasing its capacity by 50%) before the thing became unmanageably long, and I'm sure the hose would fail before anything else (added safety measure) not to mention how nice quick connectors would be (getting fancy now)...