Basically, he took management fees and converted them to carried interest, in order to secure the lower capital gains rate:

Two and Twenty. Private equity fund managers are compensated in two primary ways: management fees and carried interest. The management fee, traditionally two percent annually, is paid to the managers to cover overhead, salaries, and so forth. The carried interest, traditionally twenty percent, is a share of the profits from the underlying investments. My paper Two and Twenty described the typical arrangement. Management fees are taxed at ordinary income rates; carried interest is often taxed at capital gains rates. I focused in the article on why the carried interest portion is better viewed like bonus compensation and should be taxed at ordinary income rates.

Management Fee Conversion. Current law on carried interest is already a sweetheart tax deal for private equity, but why not make it better? Private equity folks are not the type to walk past a twenty-dollar bill lying on the sidewalk. In the 2000s it became common for private equity fund managers to “convert” their management fees into carried interest. There are many variations on the theme, but here’s how many deals worked: each year, before the annual management fee comes due, the fund manager waives the management fee in exchange for a priority allocation of future profits. There is minimal economic risk involved; as long as the fund, at some point, has a profitable quarter, the managers get paid. (If the managers don’t foresee any future profits, they won’t waive the fees, and they will take cash instead.) In exchange for a minimal amount of economic risk, the tax benefit is enormous: the compensation is transformed from ordinary income (taxed at 35%) into capital gain (taxed at 15%). Because the management fees for a large private equity fund can be ten or twenty million per year, the tax dodge can literally save millions in taxes every year.

The problem is that it is not legal. Because the deals vary in their aggressiveness, there is some disagreement among practitioners about when it works and when it doesn’t. But in my opinion, and the opinion of many tax practitioners, the practices that were common in the private equity industry in the 2000s became very, very questionable, and it’s unlikely that they would have stood up in court.

Tax attorney and professor Victor Fleischer does the dumpster diving in Gawkers Bain document dump and this is the first bit of specific skulduggery that I’ve seen as a result.