What fins are wanting to make them for? Pin style or post style? If post style, depending on size you might be able to use the Seawing nova buckles which are sold separately. If using pin style you can just tie a knot. The bungee my Novas is 7mm. Good luck.
Have you ever replaced the bungie on the Seawings, or had to?
I got a couple of those SeaWing Novas bungie straps as replacements for the Scubapro Spring straps that rusted and failed at the bolt, but shortly thereafter switched away from the SP fins they are on, so they are sitting unused, except as occasional loaners. I like the overall bungie design, and the Bungie cover is nice and comfortable even on bare feet, while the original spring's cover straps were not.
I also saw someone who was struggling to fit in borrow undesized fins one time pop the bungie out of mount on those. His side covers had fallen off and they might be part of what holds the bungie in place on those.
---------- Post added August 7th, 2014 at 07:37 PM ----------
I just used the plastic fitting that clips on the post. The first is an old image from an early experiment, but should give you some ideas. The second image is for fins without posts. The fin on the left in the side-by-side image is a Jet, and Hollis F1 on the right.
I payed with the clips and never 'saw' that looping possibility. Thanks!
What thickness of bungie is that, (on the post type)? Did you run it doubled all the way through?