If you are planning this as a tax avoidance scheme, well it is not. The gains will be taxable in your hands and not in the Banks hands. Banks simply don't cash out the stock at the same price, there will be quite a bit of both Lawyers and others ... so in the end you will end up paying more.
The link indicates that one would pay back the loan via one's own earnings.
So if you have a stock worth USD 100, you can pledge this to a Bank and get a max loan of USD 50 [there are regulations that govern the max you can get against 100].
You want to buy something worth USD 50.
Sell half the stock, get USD 50, pay the captial gains tax on USD 50.
Pledge the USD 100 stock to bank, get a loan of USD 50.
As you have not sold anything, there is no tax.
Over a period pay the USD 50 loan via your own earnings.
A high valued customer may be able to get away with a very low rate of intrest and very long repayment period.
The tax implication to your legal hier would be from the time the stock come to his/her hands to the time she sold.
So if the price increase to 150 by the time Mark dies, and its sold at 160 later, the gain is only of USD 10.
So rather than paying 30% or whatever the applicable tax rate, it would be wise to pay an interest of few percentages.