Sorry, but you are essentially re-inventing the wheel.
Hams have used multiconductor cable, like flat rotor control cable with the wires cut to different lengths as radials for years. It works!
Yup. Butternut even sells it's STR-II "multiband radial kit" for the
HF6V and 9V made with 300 ohm twin lead, notched to make various resonant
elements similar in fashion as you describe. So Window Line should work the same,
though it may take some experimenting as the other poster said.
The Butternut radial kit is ridiculously expensive! (also contains
enough plain insulated wire for a couple 80m radials)but still at $170 is insanely overpriced.http://www.hamradio.com/detail.cfm?pid=H0-004038
I've thought about experimenting with reproducing that multiband
radial kit with Window Line......and if it works well perhaps
selling them at hamfests. But I don't know how well they would
sell or what the price break would be. Hams are notoriously cheap,
and making individual band radials is easy and cheap.
Good luck with your window line multiband radial
experiments.....and please do let us know how it turns
out. I'm quite curious to hear the results, especially the
"weave a third wire as the 10 meter radial between the 2 leads of ladder line" part.
73, Ken AD6KA