Could work using the existing FAs feature... Like, opening a 2nd FA, for, 8, 16 or 32 teams that could find that Tournament Group using a #tag. The creator could add a reward, like a emblem or Jersey for the winners, and decide to collect money/tokens that could be part of the reward.
Too could be cool, allow to face the winners of 2 of these particular "prívate tournaments" .. or a big finale between 4 winners teams from 4 different tournaments.

This during the middle of da week, when we have no FAs.