Part of this already exists, as an APU
You would want to graft piping from the exaust thru the hot side of the turbine, and remove/seal up the cold side compressor componets. The problems might be the size of existing, inexpensive surplus units. You would also want to thermally insulate all the exhaust piping till you get to the APU, becuase you are acutally using the heat energy of the exhaust gas, not just its velocity.
http://www.users.zetnet.co.uk/gas/gtp30.htm
http://www.users.zetnet.co.uk/gas/lucas.htm
http://www.gasturbine.pwp.blueyonder.co.uk/newpage.htm