Placing walls beneath floating dormer walls

[modelBuilder]

I have a story-and-a-half design, with a floating dormer on a portion of the roof. I would like to put a wall directly beneath the wall on the face of the dormer, and one directly beneath the wall on one side of the dormer. The other side of the dormer would continue to "float." Home Designer Pro 14 won't let me simply place walls there. The best I've been able to do is put them about a wall thickness outside the dormer area.

Maybe I should have started with an ordinary dormer--that would probably have gotten me a continuous wall down to the floor coincident with the face of the dormer. I would still have a problem with the side walls, though. On one side I'd have to get rid of the wall down to the floor and make it float, and on the other, I'd have to add some wall under the dormer wall. Any suggestions?