Been finding out about lens nodal points... for the schools 10mm sigma lens I need to rotate around a point about 16mm from the front of the lens (6mm behind the gold band).. see here: http://www.hugha.co.uk/NodalPoint/Index.htm
going to chat to russell and see if I could make something since the tripod I've borrowed doesn't have that much adjustment possible...
Update, 29th Sept 2012 - found an interesting homemade bracket here: http://www.peterloud.co.uk/nodalsamurai/nodalsamurai.html
and a pic showing the nodal point of the 7.5mm Samyang lens I recently got for my newly acquired GH2 http://www.panoguide.com/forums/qna/10188/?page=1#msg74401
30th Sept: found some stuff about defishing images and video here: http://m43photo.blogspot.co.uk/2012_03_01_archive.html