Before I had a compressor my mate devised this
http://i487.photobucket.com/albums/r...pistontool.jpg

http://i487.photobucket.com/albums/r...lla_rax/t2.jpg

Its a bit crude but did the job,16mm socket,four slits in it so it allows the nut too travel back opening the socket and gripping the piston.We were doing it at night and everywhere was shut