Adding tubes out of plane with main triangles

I would love the ability to add tubes out of plane with the main trainagles. In addition to the tubes main diameter, it would be nice to be able to establish this tube's position fore and aft, left and right of the top tube center and have other tube connection points and mitres calcuated based on its presense.

Example: Add a tube on top of the seat tube in pararllel with the bottom bracket that serves as the connection point of the of the top tube and seat stays.