Hi Sarah,
While I note that you're keen to use the resources that you have to hand, I would offer a word of caution if using this method.
This system works if using a paddle float with no other means to secure the paddle shaft to the kayak, but it does shorten the 'outrigger' which may mean the floatation is insufficient. You will need to test it.
I used to use this system of looping around the paddle, but that was when paddle shafts were either aluminium or fibreglass. They were strong enough to withstand the load that was applied when paddlers were struggling to climb back aboard.
When paddlers started using lighter paddles, particularly those made of carbon, we had a few expensive failures. The loads were more crushing and localised, rather than the forces the shaft was probably designed for. An engineer may wish to explain that, but I just saw the resulting broken paddles.
Having said that, a few weeks ago I saw a carbon Greenland paddle break when the paddler was doing a paddle float re-entry with the paddle under the deck lines.
I'm not sure if you were planning to use it with a paddle float outrigger as shown, or a 'climb aboard' aid in an assisted-rescue. Also, does it need to be adjustable for different paddlers, ie: a guiding or instructing role, or is it to be used only for yourself? If the later it would be easier to fix the stirrup to your kayak and set the length for yourself. If it needs to be adjustable, a prussic knot makes this easy.
Here's a link to the system that I use, just ignore the contact tow part.
A while ago I derailed a thread on rescues with talk of my contact tow: http://www.westcoastpaddler.com/community/threads/back-deck-carry-with-swimmer-assisted-tow.8202/#post-89292 I've now photographed my setup, which may be of interest. This is the towline, which is short length of cord...
www.westcoastpaddler.com