Well, he could have blocked custody transfer, right?
I don't see how. He's already been sentenced. He is a citizen of Iraq; not the U.S. Seems to me a blocking of transfer would be a U.S. military decision.
If the execution did not happen already it may not happen until monday Iraqi time. There is some kind of law that they cannot execute on sat and sun. It's some kind of Muslim holiday there among atleast 2 of the groups.