<p>Much like a raft of baseball sluggers in recent decades, buyout shops have seized on a performance enhancer that artificially jacks up results, according to many industry executives. The practice isn’t illegal, and is largely cosmetic, but it allows private equity firms to goose what’s known as their internal rate of return, or IRR. That’s the most important annual performance yardstick they trumpet to woo prospective investors. Here's their strategy. </p>