mad maximus wrote:If I understand what you want to do correctly then your solution presents a number of problems when you actually need to use it. belay devices, pulleys, and other tools are designed to thread a single rope within a single mm range.
I was going to post something similar regarding pulleys, etc., but I deleted it at the last minute because I thought about whether you would actually have to pull on both ropes, or if it would be sufficient to rescue by simply pulling on one strand and ignoring the other. The climber would presumably be securely tied into both strands, whether it be with one combined knot or two separate knots.
That still doesn't mean it's correct practice; I was just thinking there would not be a problem with using pulleys like I had first thought.