Then run it
There's nothing stopping you running categories not on the boards

Whenever it comes to adding new categories to the leaderboards, it needs to be demonstrated that enough people are running it to warrant adding it to the EXT boards.

Generally speaking, if you could find 5 runners who would run this and submit videos, it would likely be considered for EXT. Past categories have been added with less runners, but if the interest has been there to run and improve it