Stuck seat post extractor tool

I once tried fixing a blade to a dowel, used a Dremelled to cut a slot into the dowel and epoxied the blade into position, but found it was really hard to a) apply enough force against the inside of the post to cut well and b) keep the dowel parallel to the inside of the post to cut evenly through it. Being more rigid using a metal rod rather than wooden dowel would help a lot, but the reciprocating saw approach gets my vote..