You create a league system based on the american model. Equal shares, etc. Basically, you offer those 20-30 teams a massive, massive financial return, coupled with the realistic(albeit difficult) possibility of winning the league, expanding their reach, increasing the fanbase and strenghtening the brand. etc.
the super league is, as it stands, viable enough to be an effective negotiating weapon for the ECA against UEFA/FIFA
If UEFA allow PSG to bullshit their way out of serious repercussions, ECA will make their move, and it will have seismic effects on the sport on the global stage.
Of course, if PSG simply generate enough money to afford what they're doing, that's another matter. ECA will be pissed, but ultimately all they'll do will be a revision of FFP to make it harder for PSG to dominate the market in such a way