Common-knowledge says that left over slivers, chunks, and grit are left in the engine from it's original mfr and the break in oil allows for collection of that crud. Perhaps even the break-in oil is slightly different than standard oil with extra lube and junk to ease this process.
Further, in most freshly built engines I've known, parts need to "match" each other for smoothest, leak-free running. This match takes a little time, and 600mi is probably a reasonable for any daily-use vehicle.
(racers will bang-em in and run, but they live with motors that are rebuilt every 3 races or so).
Besides, if it slips out that you beat it badly during break-in, I'd walk away from you if I were a dealer about to provide service.
Do what the mfr says, and if it chokes, the *mfr* is responsible for remedying the situation. Why mess with that deal?
Chris