Is there a simple way to do a "polar" plot with arbitrary angle axes?

I'd like to use a polar plot to visualize data, but the "angle" value is not actually angle. For example:

polarplot(mod(X,a)*2*pi/a, Y)

I'm just visualizing X as wrapped modulo a.

So, on my polar plot I'd like the angle axis to go 0 to a instead of 0 to 360 (or 0 to 2pi). Is there a straightforward way?