Once you understand how the 'aligned' dimension works, you'll see it's really quite easy to achieve without any short lines, hotspots or static dimensions.
The aligned dimension determines it's angle with the first two elements it dimensions to. Those first two elements set the vector for the angle and everything after that is simply placed into the angled dimension chain.
Having said that, all you need to do is continue your construction line past your boundary and then dimension in this order:
1. To the corner of the building. (Keep in mind that ArchiCAD will highlight what you have dimensioned to, so if the construction line or slab appears selected instead of the wall, keep clicking in the same spot until the element you want to dimension to appears selected.)
2. Dimension to the end of the construction line. (That will set the angle of the dimension to the angle of the construction line.)
3. Dimension to a node of the boundary. This node can be an endpoint, midpoint, or special snap point. Just make sure it is not the intersection point between it and the construction line. (Keep in mind that this dimensioned point will be associative (ie. non-static) if the placed dimension node apears as a circle. If it appars as a square, it will be static (not associated to anything), and that's not usually a good thing. If you see a square, just click on the square again and dimension elsewhere.)
Now all you need to do is delete your construction line. The unwanted part of the dimension chain disappears leaving you with not only the correct angle on your dimension, but a dimension that is associative and doesn't require extraneous 2D elements to continue to get in your way. It's clean.
Of course there are many different ways to accomplish this (for example, you could have simply used the midpoint of your construction line to set the angle vector), but I just wanted to make this easy to grasp. Keep in mind that a lateral thinking user will use this method for all horizontal and vertical dimensions to avoid the merciless horizontal/vertical dim switch!
Hope that was clear - it is much easier to show in person and if GS let us upload animations, I would have demonstrated it that way, but until then an image will have to suffice. Feel free tell me if you didn't 'get it'.
Cheers,
Link.