Garth, perhaps another alternative:
Obtain a rather long bolt with a head diameter less than the ID of the remaining seat pin portion. Place head first into frame to point below the pin. Slip on a piece short length of pipe (i.e. a nipple), follow with a large fender washer or two, finally a nut. Engage head on bottom of seat pin and use the pipe as a slide hammer to try and pop the remnants out.
Don't go berserk with this contraption because you certainly don't want to swage the #$%^& thing in any tighter. If you're careful, it should pose little risk to the frame. Happy extracting; you will win this one.
Charlie "shade tree mechanic" Young
Honey Brook, PA
> Because I have nothing to grab onto, I will probably have
> to plan for an extended campaign. If anyone has any advise specific to
> how to extract a post that has broken off below the lug, please feel
> more than free to offer it, or even to offer encouragement.