I have been messing with a climbing method that sounds similar to this. I basically use two tethers, the top tether is connected to my RCH, the bottom tether is connected to foot stirrups. I use a Ropeman 1 for each tether. Having both feet in the stirrup allows you to put both feet against the tree and makes it very stable. I sit in the RCH, pull on the tag end of my foot tether, stand up with both feet against the tree and pull on the tag end of my RCH tether. You can get two moves with the Ropeman's before having to move the tether ups. The first time I did it I went 20' in about 5 min. I also added another prussic and biner to the foot tether that stays at waist height. This allows you to stand in the stirrup and clip into the RCH harness so that you can stand up and be hands free to set a platform or move around limbs. You can basically go as high as you want with just two ropes.
I am going to mess with it some more if it ever warms up.
I have also been working on a similar technique. Two improvements.
1) If you use a long enough tether, a couple of lightweight trekking poles can be used to push the top tether farther up the tree while you are standing on the bottom tether. This makes the process a bit faster, and trekking poles can come in less than a pound/pair.
2) Tie the stirrups together with about 2-3 feet of webbing to eliminate any kickout.
What stirrups are you using? I'm using the Metolius EZ-aiders which fit snug on the boots, but they are overkill for this application.