I use my tweezers to unscrew those threaded holders.
Selecting the right size tweezers and with a steady hand, it usually unscrews easily.
Be careful not to damage the thread, and... mind you're fingers :sick:
Usually there is not much resistance in there, remember not to overtightened them either.
Or, if you plan to do this more often, i suggest you make a set of fixed tools to fit various sizes, think of a big screw driver, made of some tough plastic, with a wide notch in the middle or more like a straight spoon with a notch.
Use a hard plastic like ABS or polycarbonate.
Molding some composites for more durable tools would be an idea too.
Good luck!