"The very rich are different from you and me," wrote F. Scott Fitzgerald. That's true when it comes to new dot.com money as well as well-aged old money.

Banks are offering dot.com millionaires and other stock-laden customers the right to use their portfolio as collateral on a house,

"Our normal comfort level (for a stock-backed mortgage) would be no more than $5 million." - Jean Blomberg, Silicon Valley Bank

without having to cash in a single share.

"We do restricted stock loans and stock secured loans," says Jean Blomberg, at the Silicon Valley Bank in Santa Clara, Calif. "We don't advertise it. We reserve our banking for principals and corporate heads of companies who already do their business banking with us."

In fact, the bank solicits the business. Rather than advertising, we go to them and say, "we can do this for you," Blomberg says. In Silicon Valley Bank's case, "that means offering loans up to $3 million or $5 million," she says. "Our normal comfort level would be no more than $5 million," she adds. Click here for the art of the deal.

A low loan-to-value ratio makes the deal relatively safe for the lender. At 70 cents on the dollar, a stock could plummet 30 percent before the bank lost a cent. Pegged at just 50 cents to the dollar, the stock could lose half its value before concern sets in.

These aren't penny stocks we're talking about. The Boston Bank only considers blue chips. The bank won't even look at you if your stock isn't worth at least $10 a share. And they're usually much higher than that. "Blue chips," explains Martha Johnson, at Boston Company in Massachusetts, "are less vulnerable to market fluctuations."

Financial institutions offer these deals to their very best customers, so clients don't have to sell stock and face a stiff capital-gains tax. But the bank also becomes custodial agent for the stocks held, meaning the client can't sell them.