Is it possible to have the start angle of a spiral parametrically linked to another feature?

In my case I’m making a simple pump, but I’m not sure where the outlet is going to end up being located. I’d like to have the exhaust port drive the spiral orientation, which would define the volute cavity.  Currently if I move the exhaust port, the volute stays in the same place until I manually change the start angle.  Unfortunately the geometry is such that the values don’t work out cleanly, so a change requires use of the measure tool, and a bit of trial and error.

One attempt I made was to define a coordinate system based on the exhaust port.  My thought was that I could have the spiral sketch drawn relative to this, but so far I haven’t figured out a way to define a coordinate system for a sketch.