Brass or aluminum drifts are safer than screwdrivers for both the cups and frame. As recommended, work progressively around the cups with gentle taps and they should come out straight.
I've also heard of using a length of copper pipe with two slots cut lengthwise at 90° in one end and the resultant four "petals" spread out to slightly greater than the inside diameter of the headtube. You use it just like the commercial "rocket tool". PVC pipe similarly cut and bent with mild heat probably works too if the cups aren't too tight.