I don't think the ball bearing trick will work because there is a 90 degree turn they would have to go around. Unfortunately when the bit broke it was because it bit in too aggressively so I am thinking it either needs to be rotated in revers which I have been unsuccessfull in doing, or driven out. I will try to reverse rotate it some more to get it loose but I am not confident that will work. If it means the block is junk anyway, I may try drilling a hole just above the drill bit tip and try and drive it out. I would then tap the new hole for a pipe plug. I would then have to re drill the passage carefully past where the pipe plug intrudes.