There is no built-in program for this.
polar() looks for an existing polar grid on the current axes and skips drawing the grid if it is there. plotyy() creates a second axes to draw in, so the grid would not be on that axes, so the grid would be fully plotted again, interfering with the appearance of the other grid.
In the past, I have picked apart how polar() works, and sometimes I even remember how ;-) I could probably come up with something not bad looking. Where, though, would you want the additional axes to be displayed? And should the angles be the same for both, or is one axes tilted relative to the other?
