It's hard to say what the best solution to this is, because you're absolutely right, many billionaires don't spend "money" - they leverage their assets to get stuff. If they need to liquidate anything, someone that monitors some portfolio at some wealth management firm will do that with a few clicks and some signatures.

Perhaps the best option is regulation of a banks ability to finance against leveraged assets above a certain threshold? I'd also be for a cap on CEO salaries and bonuses, perhaps with both shareholder and employee approval needed to execute executive bonuses. I imagine that alone would mean most CEO's would lose a fuck-ton of money.

I'd love for a wealth tax to be viable, but it would require balls of steel from the president, and a central tax authority that won't be coerced into accepting loopholes. Even then, it would be hilariously easy to get around by moving wealth elsewhere.