|Back in the day when i used to top rope solo i used two separate ropes for redundancy.
On my main rope, I used a petzl microscender which works very well in my opinion. The device was attached to donut on my harness via a steel mallion, which had abit of elastaplast tape wrapped round it in order to prevent it from crossloading. This main rope was also my abseil line.
The backup rope, had alpine butterfly knots tied into it every 4m or so. When i climbed to the first knot, i would attach one end of a quickdraw to the knot, and the other end to the donut of my harness. When i reached the second knot, i would do the same with a second quickdraw. When i reached the third knot, i would unclip the first quickdraw from the first knot, and clip it into the 3rd knot, and so on... By doing this, i was always clipped into a knot no further than 4m below me, which was good enough for my piece of mind given it was just the backup rope anyways.
Yes it was tedious, and yes i would get more pumped phaffing about with quickdraws, but the purpose of tope rope soloing for me was to build climbing endurance, which it certainly helped to do.
It was tempting to use just one line, making the whole setup quicker, easier, and the climbing more enjoyable, but for the sake of safety, i opted to phaf about with quickdraws and knots.
- my two cents.