You could use two magnets to accomplish this quite easily. Make sure that your files are saved. Opent the character without the helmet. place the magnet base just inside the ear and make sure you keep the base small and the zone to just effect the area right around the ear. Then all you have to do is move the base in the X direction to lul the ears in. Since the helmet will cover this area you do not need to be too neat about it. Just make sure that the magnet fall off zone is small as not to effect the rest of the face. Do the same on the other side, hide the magnets. Put on the helmet and your good to go.