Are angel investors, fund managers and even some retail investors getting in on the back end of privately held multibillion dollar startups by snatching up shares from employees and stockholders now?

A story published today by Fortune says yes, and names super-angel Chris Sacca as one of the more aggressive buyers in the space.

According to Fortune, Sacca has created two institutional investor-backed funds, Industry LLC and Lowercase RT, to quietly buy up Twitter shares from employees and preferred stockholders. Those funds are in turn part of a $30 million pool of buyout money that has allegedly been raised to focus exclusively on buying Twitter shares ahead of any impending initial public offering.

Although Twitter shares are difficult to sell on the secondary market, Sacca seems intent to target the company — perhaps simply because he’s in a good position to do so. He’s one of only a handful of people who has a special agreement with Twitter management, and since he invested early in the company with his own money, he still functions as a company advisor.

Both Sacca and Twitter declined requests for comment from VentureBeat today.

Still, the idea that all tiers of investors are looking for early entry into these marquee-name, privately held companies by using a largely unregulated secondary market as a conduit is an interesting theory.

It is also a stratagem that has not gone unnoticed by Sacca’s peers.

Fortune cited unnamed sources that said several similar funds have recently been raised by other managers to snag shares in companies such as LinkedIn, red-hot gaming star Zynga, Facebook and eHarmony.

The story named New York-based Felix Investments, which was launched in 2009 by the former New York head of venture capital co-investment firm Advanced Equities, as one of the funds currently following Sacca in this backdoor approach. An executive from Felix declined to comment to VentureBeat on Friday.

Thus far, sources said, Felix has managed to get hold of around two million shares of Facebook stock. That figure, if true, would surely make notoriously close-handed founder Mark Zuckerberg blanch.

So why would employees and shareholders at these firms quietly sell off their own stakes within a few quarters of the companies going public?

The answer to that, says Fortune, is simple: If these sellers chose to go the retail route when selling, they’d be hit with massive costs from every angle, from management fees to closing costs. But by selling to someone like Sacca, they see only the usual “2-and-20” typical of these types of buyouts. And that, as Fortune put it, means a “bad bargain from a firm like Felix may be better than no bargain at all.”

UPDATE: The original version of this story by Fortune named Felix Investments as a unit of Advanced Equities; in fact, the firm was founded by a former Advanced Equities but has no affiliation with the company currently.