AutoCAD Inventor :: Dimensioning Angles In 3D Sketches

In the course of working up a tooling proposal, I attempted to replicate a 3D part from a customer print. While doing so, I noticed that 3D Sketch will not, under any circumstances that I can find, allow an angular dimension between a line and a plane. The customer print has two pipes projecting at odd angles from a base flange, one of which has an elbow. The print lists datum dimensions for the open pipe ends and the elbow, and gives vertical and horizontal angular dimensions to define the directions in which the pipes emerge from the flange. I have defined these three datum points in 3D space without any trouble, but Inventor 2013 will not allow me to define an angle between these sketchlines and the XZ and YZ origin planes, or between these sketchlines and the faces of the flange base I've constructed.

I am currently waiting on a proper 3D CAD model from the customer, and I'm considering longhand trigonometric calculations to place these lines properly, but I find it very hard to believe that Inventor is incapable of constraining a line to lie along what is effectively the surface of a cone.

Using:
Inventor 2013
AutoCAD 2013