OK, this started as a joke over on the MCB, but before I finished making what was going to be a remark this interesting possibility wandered into my head and I'm not sure but I think I just might be on to something...

steam engine turns compressor pump...
compressor pump fills HPA bottle...
HPA bottle is connected to marker as usual...

my god man; you have revolutionized the back pack idea!

just got to use an electric element to heat the water and fill
your "Batman" utility belt with capacitors/batteries to run the whole rig...


you know the sad part...
that is just crazy enough that it might work...
only electric motor turns compressor pump in back pack filling HPA bottle/tank
which in turn is connected to the marker by remoteline...

kind of like that gun NPS came up with only move the compressor off the gun into a back pack with an HPA bottle to work as a bulk reserve, say 13ci should be good enough...
even if it needed 3 or 4 of those big 6V or 9V lantern batteries, in a back pack
that is more or less reasonable...
hhhmmmmm.........
gotta talk to a buddy of mine that is into Marine Robotics...
i just might be on to something here; good lord this post started as a joke, now i just might have a great idea...

oh crap...
not even finished the post and the Gardeners patent ambushed me!
now here is the real Idea and Mr.Kaye if you could please offer your insights it would be appreciated, OK here we go:
you take the compact compressor like the one used in the NPS marker
have it fill a 13ci HPA bottle to say 1500PSI enough to keep the hungry markers chugging along but small enough to keep the pump run time short.
this goes into a pack pack with a rechargeable battery/capacitors to power the pump and the electronics needed to turn the pump on/off when the pressure drops below a preset level.

the big problem with the NPS gun was that putting everything on the gun made it very heavy
the batteries were small so only had a short cycle time; over all the gun was only good for half a hopper of paint then needed a recharge.
move the compressor/bottle/electric source off the gun,
put it in a back pack where the load can be better dispersed and is easier for a person to carry and we just might have a Paintball fill rig that never need to be refilled with any gas as it will just pull air in from atmosphere.
OK, the batteries will need to be recharged, but I'm sure that there is battery technology that i am not privy too that will work for this application.
if you could get a 4 hour duty cycle;
continuous operation for 4 hours similar to many gaming laptop computers,
because the compressor will not be running 4 hours continuously because of your reserve take and the pressure switching electronics
a person should get a full days play out of a single charge, or maybe even longer.

Engineers of the A.O. examine this idea, offer your thoughts, suggestions, pertinent information on small/micro compressors that could do the job, switching mechanisms, battery/compressor power sources that may fit the need...

please keep everything positive and contributory.
this might work, it might not, but it really does seem possible.
but this is not my area of expertise, and I don't have the $$$$ to experiment with the idea.