It came up in this thread, so I thought I'd post a quick tutorial.
It is possible to align the end of any kind of sweep in 3D to another building component.
Building components can be real 3D objects such as walls, but also Surface Pattern lines or model lines. Only thing is that the alignment plane needs to be perpendicular to the path of the sweep.
It's even possible to align the face of the sweep to the face of its host (something you would normally do with the "offset from wall parameter")
I use this a lot since it's more secure then stretching the blue dot and try to place this in the correct place manually.
See attached for more details.