wow, that much, i was expecting 10 - 15 psi. Then yeah, it may be doable.
First off, I'll say this, TRY AT YOUR OWN RISK. I was just playing, but I don't consider this a reliable setup at all as i tested it. In theory, if you can use as high as 40 psi, then some autococker LPR's are defintly capabable of going that low or lower consistantly (that is the key term here).
I just set up a little test system, using only an air bottle (still had 2500 psi in it, set to an output of 650psi), an ASA with an on/off and an autococker LPR (low pressure reg, in this case a shocktech FGP for those knowledgable of such things). using the the asa on/off and delicate adjusting of the LPR it was pretty easy to get it down to 1 bubble per sec. HOWEVER, at these settings, its very easy for the knobs to move and in this case, a 1/16 of a turn went from 1 bubble per sec to 100. I would also be very concerned about pressure building up behind the LPR over time, which will also increase your output.
That said, here is where I would start testing. Depending on the LPR, its output and its ratio, you may be able to get away with just the lpr and a pin valve. I personally wouldn't do it that way. Instead, I would add a secound reg, either a standard inline, or for ease, a female inline like a thor or stabilizer. The reason I would do this is because then you can reg the input pressure to the LPR down to a much more comfortable and reliable 250-300 psi. Although LPR's like Palmer Rocks and WGP's can easily handle unregged CO2, many of the newer LPR's will not like it, especially long term. with a female inline, you can just screw the LPR in directly; with a male inline, you will need two asa's, one for the tank and one for the reg. I would also be sure to either use an old WGP LPR (the ones with no external adjustment, but because of that theres a lot out there that people will just give away free since you can't hardly sell them. A bit of a pain to tune and adjust, but actually a very solid reliable reg and well suited for this type of work and I think they will go down that low, I will do soem checking) or get an extra nut to tighten down to make sure your lpr doesn't self adjust (beleive me, It can and will happen, some LPR's like older ANS are absolutly notorious for it). Defintly a system to keep an eye on though, very easy to develope leaks or bad seals. Another thing to be aware of is that LP hosing in paintball is typically 1/16 ID. thats a good bit smaller then the standard aquarium airline so you will need to do some planning on your fittings for the needle valve since that will be much easier to find fittings for then to try and go up in size on the LPR fittings. However, I notice Rex's Needle valves are 10-32 threaded, which means many common LPR's could have it attached directly.
you know, I really wish I would have started tinkering with this BEFORE I ordered a pressurized system. Still though, I definatly think long term a normal pressurized system is a better value. Rex, I might have to get one of your pin valves just to play around with.