Ask the mods directly over discord if they are willing to add the categories after you have done the runs.

I used the same line of argument but the consensus seems to be that not boards should be first but interest in running it. Id just make boards for every category including all lobbies ngl. Dont think its really a shame if a category stays empty.

Not likely at all. They generally want to make sure that the boards won't stay empty forever which would probably be the case with full clears. I recommend talking to the moderators directly tho. Iirc they refused to make a beginner lobby arb category for sc2020 despite someone having done a run. Might be different this time around who knows.