Via Buster Olney, the Yankees tried to work out a sign-and-trade scenario with an unknown team that would have netted them Grant Balfour. Joe covered this exact idea back in December, though it was framed around Rafael Soriano. Basically, some team with a protected pick would sign Balfour and them trade him to the Yankees for a prospect that is equal to or greater than the value of the pick they gave up. Balfour would have had to consent to the trade per MLB’s rules since it would have occurred so soon after he signed.
Obviously this all took place before the Yanks agreed to sign Soriano and Balfour went to the A’s. I’m guessing that once they couldn’t get a trade for Balfour worked out, they decided to sign Soriano. If you’re going to give up the pick for the reliever, at least make it the best one available.