Split level roof & inserting windows into wall / partition

I have a split level roof with a vertical section exposed to external (wall) but below it's a partition - in Hevacomp you could use vertical infil and insert rooflights for windows - my question is how do you do that in Openbuildings ?  I've seen Shane's item on

"Wall with internal and external surfaces"

however it made little seen to me as my "wall" is shown as a partition on my model.

Any ideas ?

Cheers Graham