He was literally never optioned to the minors, so from a technical standpoint he has them all. Granted he has played long enough where he could refuse an assignment and elect free agency, but then he would lose his entire contract I believe.
You do realize even a season putting up a 4 ERA while putting up a starters load of innings is a big win for $15 million over 2 years and would definitely garner a return on the trade market.