What you can do is that, you find someone in the supervisor list, who will be your main supervisor.
Then you find someone who is not in the list, but who is working in the area in which you are interested. He can be your co-supervisor.
Then you just work with your co-supervisor.
The only things are that, first of all, your area of interest cannot be too remote from the areas that are allowed by NGS; and second of all, your main supervisor must have no objection to that.
－