In IE3D help, you can find how to define finite ground plane.
In the basic parameter menu, use sigma=0 for Ztop=0; it means that there is no infinite ground. Then you can define all the layer you need (please see the manual of IE3D).
Please find the file: c:\zeland\ie3d\ie3dlibrary_examples\crescent_patch_shifted.ie3 file for IE3DLIBRARY. It is more complicated than the monopole. The structure is object-oriented and fully parameterized. You can just take out the object for the circular circular hole and change the aspect ratio of the elliptical patcha nd it becomes the shape matching your monopole.