Okay, I think I've solved this.
Just turning on the wrapping-at-ends doesn't work. It doesn't wrap the problem end because another wall is joined to it, and if you dissallow join it wraps all the way across between the stud cavity.
I made a new family based on Generic Model wall based.rft. I added a wall closure plane parameterized with a depth off of the wall face. Set this depth to match the different thicknesses of your two wall types. I added a rectangular void that cuts the wall and is parameterized for width and height (in the project set it high enough to get cut by your view range's cut plane). Set the width pretty narrow and move it right over to the end of the wall.
For some reason it fails if I try inserting it into the curved wall, but it works at least in this case of one curved wall butt-joined to a straight wall because I can just place it into the straight wall without problem.
I'll attach the family after the screencast for you guys to play with or improve.