With great difficulty unless--*polar* is actually an ordinary cartesian axes with the transformation of coordinates from the input r,theta to x,y for plotting.
The radial spokes of the axes you see are thus just additional lines, not actually any real objects related to the polar coordinate axes they represent at all. And, the angle labels are text objects drawn at the [x*cos(t),y*sin(t)] coordinates in x,y space of the (invisible) axes on which it is all drawn as well.
Unfortunately, unless they've done it finally in the new HG2 release, TMW has never built any actual objects of any sort for handling polar, cylindrical or shperical coordinate systems. You've got to do it all from scratch if it isn't in the provided routines (which are pretty rudimentary, granted).
You might search File Exchange and see if anybody has provided enhanced versions.
