To improve the design presented in the above video, you could first line your scupper hole with pex tubing.
This would further protect the scupper hole from any potential damage secondary to a metal rod running through the middle of it.
Modify the below method below by shortening the length of the pex tubing to allow for the scupper plugs used in the transducer scupper mounting design posted in the above video.
Length of pex tubing for your application = length of scupper hole - 2(length of scupper plug)
For one scupper, just one foot of pex tubing would be all you needed (would be around $1)
To completely reinforce and reline your scuppers you need the following:
1. PEX vinyl tubing---in the plumbing/lawn irrigation section of your hardware store
I chose PEX tubing over polyethylene irrigation tubing because PEX is stronger and more flexible
I chose PEX over PVC because it's lighter and PEX tubing is easier to wedge/shimmy into a hole.
--suppose you could also use just a regular garden hose if it's diameter is close to your scupper hole diameter
3. Something to cut the tubing (metal snips work, PVC cutter would be better)
1. Measure the inside diameter of your scuppers (mine were 1 inch) I had some 1" PVC laying around and it would not quite fit inside
2. 7/8" PEX is available online and probably would have been perfect for my kayak's scuppers, but HD and Lowe's had 3/4" PEX so I bought 5 feet of it for about $5
3. Lay the kayak on it's side and Place the PEX tubing inside the scuppers and see how long each individual segment needs to be to completely reline the scuppers without protruding beyond the top or bottom of the hull and then cut the PEX
4. Shoot a generous amount of LEXEL inside the scupper from the top and bottom. Put the corresponding PEX tubing piece on your non dominant pointer finger and shoot a bunch of LEXEl all around it.
5. Place the Lexel covered PEX tubing piece inside the lexel laden scupper hole and rotate it around 360 degrees clockwise and counterclockwise to get thorough coverage and remove the PEX piece from your finger so that the PEX piece stays within the scupper.
6. Smooth any lexel so there is a nice seal at the top and bottom of the LEXEL/PEX lined scupper hole
Also, make sure lexel didn't get inside the PEX tubing so you still have a functional scupper. (easily removed in the first 10 minutes with your finger or wooden dowel rod)