I also think that the photographic evidence idea is brilliant!
Hope you don't mind me saying this, but I'm pleased you're not going to keep going to SW to get weighed while doing exante. I used to do SW, and often I was given the feeling that I wasn't doing as well as i should have been, especially compared to some others who had the pounds dropping off them! It makes me wonder if they really were following the SW plan?? I used to come away having had a 100% week, but being made to feel really bad that I hadn't lost enough weight.
Good luck with the new weigh in system, I'm sure you'll do brilliantly well with this new focus!