Well in order to continue my habit of replying to myself... :) Here is a "finished" version where all the functionality seems to work. Note that when you shift in "normal" mode, the selected text is quite happy to head up to the line above. I originally thought this was a bug but now I am starting to use this 'feature". ;)
The keys are initially mapped to <Ctrl>9 and <Ctrl>0. Get it here:
http://mavis.anu.edu.au/geany/shiftcolumn-0.2.tar.gz
It does need testing, so please let me know if it breaks anything for you.
Thanks
-- Andrew Janke (a.janke@gmail.com || http://a.janke.googlepages.com/) Canberra->Australia +61 (402) 700 883