The reusing of the multi step aider is what is causing me pause about the setup. While the use of multiple aiders is an option, I do not like the idea of leaving them behind and possibly flapping in the wind. Using the tether is an option, but I find it clumsy and could interfere with the stick or Step (both would be set as high as you could reach). But I may have a solution. Bare with me, I am going to try to visualize it for you guys.......
I think this would work with the Step, not sure about sticks:
Picture a length of webbing that loops around your foot but can be cinched tight so it does not fall off. The other end of the webbing almost goes to you knee and at the end is a hook; much like the one RS and others are using for their OCBs/strap arrangement. This end is strapped around your leg just below the knee. So as you climb the aider and get one step below the Step (and maybe a stick) you hook onto the step. So you have moved the load onto the "aider" that is strapped to your leg and allowing you to easily grab the multi step aider and bring it with you as you step onto the step, then set another step.
As sketchy as it sounds, I think it would be stable.