I once towed a canoe with a family (2 adults and one wild child) across the river here in town. The water level was high and they managed to get swept downstream and did not have the gumption to get back across to their car. I can along, saw their problem and offered to help. To tow them, I used my rescue rope which has a carabiner tied to each end. One end was attached to their bow line and the other was attached to the rescue ring on my pfd. I wanted the line attached to my pfd in case I needed to release myself and do another form of rescue. The child was allowed to run loose in the canoe despite my request for the parents to hold on tight to him. They didn't so I wanted to be ready. I towed them cross-current across a strong current. Their canoe towed easily as it was stabilized by the current and their body weight but it was a major effort for me as I was the only one doing the upstream work.

If I was you, I would tied the single to the stern at closely as possible using a quick release knot which could be undone by the rear paddler by yanking on the attaching rope via extra length. I know there is a way to do this, just can't quite remember how to do it. Also, add about 100-lbs of weight (gear?) into the single )evenly balanced to give it stability. Hope this helps. At any rate, that's exactly how I'd do it.

Robert N Pruden