tl;dr: margin loans against their portfolios which are interest-only indefinitely and don't require the shares therein to be sold unless their cumulative value

tl;dr: margin loans against their portfolios which are interest-only indefinitely and don't require the shares therein to be sold unless their cumulative value is worth less than the loan "regular" people do similar financial engineering all the time with home equity lines of credit (i.e. taking out loans against the equity in your house). instead of passing down fat portfolios, they pass down real estate (which is becoming increasingly expensive)