Georg,
Careful. Cranking down the ejector stop screw on the ejector stop spindle may just burr the shaft and make matters worse. (M2's don't have magazine cutoffs they have ejector stop assembly's :D)
I think the basic idea has merit but i would just tighten the screw lightly. Flood the assembly with penetrant through the stop screw hole and then see if it can be loosened up.
The annular groove on the spindle is not on center so if the spindle has been swapped end for end the groove won't be under the stop screw hole it will most likely be out of reach.
One possibility, which i guess would be the last resort, would be to remove the action from the stock and bore a small diamter hole through the bottom of the receiver into the tunnel for the spindle. This may give you a purchase on the end of the shaft and allow it to be levered out. the hole would be invisible once the rifle is reassembled. If all else fails let me know. I will take my m2 apart and give you dimensions for where the hole should go. Aagina i wouldn't try this unless all else fails.:beerchug:
Regards,
Jim