Yes, an opt-out is also something he could have negotiated. I posted this stuff in the major league thread yesterday, it was less than an hour between Gelb reporting that he'd refused the assignment and the report that he'd signed a new minor league deal.
I'm sure it still hurt that no team wanted to claim him (let alone trade for him). He was DFAed five times in 18 months but the first four times he got claimed or traded because he still had options.