While I do not have any idea how to make something like that, I hang weight and when I’m done I slide 4 or 5 head rings on my cock with the smaller one near the glans to "lock" the others in place. The weight of the rings depends on how many you use. The ones I use are 5 or 6 gauge and have an internal diameter of 30mm. When I wear 4 or 5 of them the weight is roughly 8 oz. It’s not a lot but it’s a constant pull after hanging.
There are magnetic ball stretchers that can weigh up to 900 grams. I haven’t tried that yet as I fear the internal diameter of 36 mm may be too big to keep it in place while flaccid. For now I just use the rings. They give a nice tug and the shaft seems to stay a little larger due to the weight and I love the feel of the weight and how it slaps against my legs.
I know it’s not what you are specifically looking for but they are much more cost effective and you can get a feel for what you do want. Good luck.
Link to the type of stretcher I’m talking about. Idk if it will work or not.
https://www.ama … /dp/B09NGWBS6F/