It looks like there is no “escape hatch” for admins.
If you set the approval posts to 1000 the first 1k posts will need to be approved even if the user is an admin.
I don’t think this makes sense so I added it:
https://github.com/discourse/discourse/commit/fb7baeb7a2d3d44c81fb8dc8bc311e1af1f45bae