Sam,
Thanks for the post.
You have two options and this depends on the size of your fin.
As meesier42 wrote there is a loop where the bungie goes through the heel pad on the back of the heel pad. You can thread the leash loop through that loop.
Another option you might try is securing the leash loop around the molded foot pocket and then attach the webbing around your ankle. It most likely will fit, but you need to test this out and make sure your ankle will be unrestricted in movement. I have used it this way in certian situations and it will work.
Curious are you diving, body surfing, or fishing?