You are thinking inside the framework of law and regulation. I wouldn't say it is impossible. The Won just orders Geithner not to issue the checks - stroke of the pen, law of the land.
The counter to that is to tell the people "He has no authority to do that! SS has it's own independent funding source! He's embezzling the SS funds!".
The fact that the Repubs are NOT making noise about that has me suspicious, in a "the dog that did not bark" sort of way.