my bro in law batters them out with my sds drill ,i did see somewhere on an american? site a remover using stock gas? fitting pieces which looked interesting perhaps it can be adapted if the sizes vary in bushes.
i had lost the link but a search found it again
http://www-ese.fnal.gov/People/wilce...shing_tool.htm
whether the parts are available in the sizes mentioned i have no idea but perhaps we have a resident fitter to advise?