My glass guy used a lid to like a glue bottle or caulk or the like. You know the type like a long narrow funnel. The end was cut off enough that the rope can move freely through it. He uses spray silicone or foam glass cleaner as a lubricant be generous. He just slides it along the groove leaving the rope in the rubber. It happens fast.
An old trick of the trade,it's what I use,i'd be wary of silicon spray though,apart from the implications of later paint problems it can get to the point it is almost too slick and will fight you.
I use an alcohol based glass cleaner concentrate that I mix with plain old water.
