I have an idea: Anyone "earning" more than $1 million per year pays no Federal taxes. At all.
Instead, they just have to spend at least half of their "earnings" on goods and services. Every year. I don't care what they spend it on: Could be yachts, could be Oreos. Could be Chinese-made trinkets or American-made binoculars or Italian sports cars.
Don't care: They must spend it on goods and services. Not domestic investments. Not off-shore resources. And then prove that they've done so, every year, and prove that they've received these goods and services, and that they were all sold to them at reasonable market value.
(This likely means they'll need to employ an accountant. Cry me a river.)
In exchange, they owe no Federal tax. (I'm also in favor of saying they'd owe no state taxes, but that's 50 more arguments.)
The other half of their "earnings"? They can invest it. They can sit on it in an interest-bearing account. They can buy even more goods and services. They can have the bank give them 50% of their earnings in $2 bills so they can swim in them. Give it to their children and friends. Donate it to charity. Buy small countries. [More] Hookers and blow. Don't care.
If they fall short on spending 50% in a year, then they simply owe the remainder and a 25% penalty to the general fund: If they "earn" $1,000,000.00, and only spend $300,000.00, then they'll be required to put $250,000.00 into the kitty.
Hoarding thus solved, and their contractors and retailers thus wealthy (though perhaps not rich) and paying regular taxes, the wealth disparity is thus solved.
If they don't like this gambit, they can just, you know, earn less money. And then it will still automatically be spread out much the same by market forces.