I know you want a response from SNM, but thought I'd contribute to what I do.
I change the # of mins for the dvd I'm doing if I do a premix. For example, for BM2 I did the cardio blast premix....I changed the minutes in the WM to the # of minutes that the premix was and then it automatically recalulates the calories burned.
For ab segments, I just put the Ab Hits dvd in the WM and change the minutes to 10 (or however long you time the ab work you do).
HTH