1. Work at a startup

If you're an entrepreneur, you can create more than one share class of stock at your company and put $1,000 in a standard or Roth IRA, said Bill Parish, president and chief investment officer at Parish & Co., an advisory firm based in Portland, Oregon. If some shares are valued as low as $0.000001, as Yelp Inc. reported in its S-1 filing with the Securities and Exchange Commission in 2012, that can buy a hefty chunk of equity.

"The key is that you transfer the stock directly from the company to your IRA," Parish said.

As the securities appreciate, investors can sell and diversify into other holdings tax-free until they withdraw funds. Or, in the case of a Roth IRA, the gains aren't taxed at all, Parish said.

Max Levchin, chairman of San Francisco-based Yelp, reported 2.7 million shares of the company's Class B Common Stock in his Roth IRA, according to this year's proxy statement. Class B shares of Yelp are convertible at any time by the holder into shares of Class A on a one-to-one basis, according to the filing.

Yelp shares closed at $76.54 in New York earlier this month. That comes out to about $206 million worth of Yelp shares in his Roth account.

At the time of the company's S-1 filing in February 2012, Levchin reported 3.9 million shares in his Roth account.

Photo: Max Levchin.

2. Start at a Low Initial Value

The next strategy involves placing a low initial value on an IRA's investments.

Romney, the co-founder of private-equity firm Bain Capital LLC, never explained how he accumulated so much wealth inside his IRA. Yet one way that private equity and hedge-fund managers build large balances is by valuing their company's investments at close to nothing, and they later grow exponentially, said Bobbi Bierhals, a partner at McDermott Will & Emery LLP in Chicago.

3. Work for Yourself

Self-employed people including doctors and lawyers can contribute as much as $52,000 this year to their IRAs. If you start at age 25 or 30 contributing the maximum amount, you don't need extraordinary investment returns to end up with millions by the time you're 50, Bierhals said.

4. Avoid Diversifying

Use a self-directed IRA to make a big bet on a closely held company, said John Olivieri, a partner in the private clients group at White & Case LLP. If the business succeeds, the IRA's value can increase dramatically, he said.

"Those clients who don't diversify an IRA, but instead invest the whole thing in one stock or venture that does really well, will have very high balances," Olivieri said. "Of course, they could also lose everything."

5. Sock Away Plenty in Your 401(k)

Sometimes the tried-and-true way to retirement security works.

Employees of a company with a generous 401(k) program can end up with millions in their account over a career and then roll it into an IRA. Company stock appreciation, annual matching contributions from the employer and additional profit sharing can all add up over a career.

"You can expect some people to have multimillion-dollar IRAs if they include funds from rollovers," Parish said.

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