I have used a rope saw in the past to remove formers,get some pull pull wire or steel fishing leader and make a rope saw don't get the plastic coated stuff ,wrap it around some good size wooden dowels and start sawing ,i have used this method to take old air tanks out that were hysoled in also the good thing is the cable can be as long as it needs to be say from the wing tip to the root so you get a nice flat pull