Good luck Graham!
I have a modded 40D and it's a new world.
I have had success with doing many light frames and then at the end of the night, take the camera off and put the Canon bayonet cap back on and set it to do 25 or so darks using the little hand controller while I go to bed. The Exif delta from start to finish is only about 2-3 degrees over my entire session at worse. There's some very interesting reading about dithering and ICNR vs separate darks. Do a search around
Unfortunately for me, I don't think I can dither with my Nexguide as it simply locks on and that's it!
Stick with what works best for yourself!
Darrin...