Much smarter people will need to work out the details, but I think that closing the capital gains loophole would be a good start. Basically, if a person wants to leverage their stocks to take out a loan, then they get taxed on that amount. We can have a minimum amount before it kicks in such as a million dollars to allow small business loans and other things to still occur.
I understand we can't tax peoples unrealized assets, but it's bullshit that unrealized assets can then also be used to gain real monetary value.