I've got a really simple solution, but it's hard to explain in print, and I don't have any pictures (and can't take new ones, I don't use the two-hander anymore and re-purposed the components), but I'll try.
Take a Pringles can and paint/tape/whatever it your color of choice. Put two leather bands around it at the top and bottom, and affix those to a long strap of leather (preferably, but not necessarily) that runs perpendicular to the bands (along the can). Secure the bands to the can with Chicago Screws (this is so that you don't have to re-make the entire thing when the the can finally breaks/loses it's shape). I used one screw per band, 180 degrees around the can from the straps, and that worked fine. The length of the 'long strap' will determine where you want the two-hander to sit, so you'll have to figure out that length for your body. So, on one end of the long strap is the pringles can, the other end should terminate in a belt loop. I recommend a straight belt loop rather than an angled one (which is what will seem intuitive if you're used to making armor pieces) because it's easier and doesn't seem to make any difference. Effectively, you now had a pringles can hanging from a belt that is hanging from your belt. Sweet. This is part 1.
Part 2: Take a metal ring (about 1" or so) and attach the end of a leather strap to it, probably 3-6 inches long, with a hole punched in it near the other end. The size of the hole will determine how easy/hard it is to pop your two-hander free. I used about a quarter inch punch, and that worked pretty well. Remove the waylay end of your two-hander and put the ring around the core so that it moves freely about the grip area on your two-hander, then put your weapon back together.
Part 3: On the shoulder of your armor (right shoulder if you're right handed, left if you're left handed) affix another ring. Figuring out just where is comfortable for this is a personal choice, but you'll figure it out. On this ring put one of
these pins. You'll need a pretty big one, about 3 inches. The big loop of the pin goes in the ring.
That's the entire construction part. Here's how it works:
Put your two-hander in the pringles can, point down. This is easier to do if you sweep it to your left side so that you can see it, rather than fishing around for it behind you. Then, as you swing the weapon back around you, grip only the leather strap on the ring on your handle. The ring will slide up along the handle as necessary. Put the pin (the squiggly side) through the hole in the little strap on the handle. Your weapon should now stay in place on your back.
When you draw the weapon, grab the lowest end you can comfortably reach and pull it directly up so that it gets free of the pringles can, then pull forward and down, using it like a lever with your shoulder as the pivot point. The pin will let the strap free since you're pulling it along the release axis. The weapon should pop free with a minimum of effort, and looks and feels very smooth.
If you are too short to pull the weapon all the way out of the pringles can, shorten the can so you don't have to pull it as far. For stability, leave the can as long as you can though. (A duct-tape roll does
not work.) The can will probably hit you in the upper shin while you fight, but I haven't found it long enough to actually trip me up of impede my fighting ability (and although I'm 6'3", my two-hander is max length, so this may still work out for you). Generally, the only time the two-hander pops off when I don't want it too is when moving through branches and snagging it. Most combats it stays fine (but that's not an issue if this is your primary weapon, it wasn't mine, which I why I eventually stopped carrying it (the spirit linked shield didn't help, either)). At some point, you
will crush your can (though it took me a couple of events). Always have a backup. (Mine usually contained Pringles).
~Matt