If one considers the tank as upstream from the regulator, then anything
downstream of the regulator is used to running on regulated 11 inH2O
pressure.  One can buy an 11 inH2O regulator that attaches to your bulk
propane tank and can be connected to a suitable propane hose to feed all
sorts of stuff that needs that pressure to work well.

Now if you put an additional manifold (that rectangular brass block to which
the downstream tubing attaches) or a suitable tee in the circuit you now
have an additional port to which you can feed the 11 inH2O output of the
bulk tank and regulator.

This is fundamentally what the extendastay does albeit upstream of the
regulator.  Lots more room downstream AND you can run unregulated stuff off
the tank and regulator since the output is downstream .  A venerable
catalytic heater is one you can plumb into the system.

These often sell for $20 or so on EbaY and deliver a pleasant radiant heat
to ward off the morning chill while you brew the first cup.

Disclaimer:  anything you do with propane can kill you stone dead.  The
missive above is merely a hypothetical untested unvalidated unverified
theory, not a set of instructions or recommendations.