I've dealt with similar things. Used something like this:
http://www.tooltopia.com/schley-68450.aspx
Well, i bought some aluminium tube, sharpened the end until it was like a blade, then slipped it down, quick tap down on the end of it to cut the seal, and pulled it straight out.
Dealing with broken-off coil packs isn't fun either. Had a few of those, where the coil pack itself snapped off the top of the boot. Used a flat piece of thin steel, sharped the end and edge like a blade and tapped it down with a hammer to slice through the rubber. Used a screwdriver to break the two parts of the steel casing.