Just tax them.
For example, the limit could be $30,000,000 so if you're making more than that in pretax income, your income would be $29,999,999.999 etc. with the fractional cent increasing so people could still compete on a scoreboard.
Also, it seems like one of the biggest arguments against capping wealth is that it would disincentive innovation. But just about every person who became billionaires through innovation never had that intention to begin with. I firmly believe Jeff Bezos would still be running Amazon if he had a wealth cap. Mark Zuckerberg would still be running Facebook. No?
Examples include: Your data, subsidies from your tax dollars to create asymmetric markets, common things like water quality or environment, or legal asymmetry that allows for rent-seeking.
I don't want Billionaire to feel forced to give "true gifts" through social pressures or otherwise - I'd prefer if their wealth was properly utilized through a just level of taxation.
Why'd you need so many words to say "taken?"