Programming an element similar to y axis icon, c#


I am seeking some initial advice regarding the production of a display element similar to the axis icon (the graphical element that floats in the lower left corner of a perspective view-port. In particular I’d like to produce or mimic the y axis of the axis icon to provide a graphical illustration of ‘north’.

I have experience with producing heads up display elements and the display pipeline class, so my question isn’t about the nuts and bolts of that. More particularly I guess my question is the following…

Knowing the location of a 2D point on a near plane to the camera that could be considered the origin of a north arrow for a heads up display, what would be the most effective way of casting a y axis equivalent to produce the correct line for a north arrow assuming that north runs along y? Do I need to cast the 2D point back into 3d space to achieve the transformation or is there a more efficient way of achieving this - for example by accessing the axis icon class?