I don't know .... this sounds like a trick question ... but have you considered using a countersink bit? If that hole is for a standard screw head it's probably a 82 degree countersink which you can buy at most tool suppliers.
I have a side business manufacturing front panels for electronic enclosures (Protoplates), and after having made many panels for many different customers, and a lot of grief, I'll share with you something that I have learned the hard way: the fastest and most cost effective way to make countersink holes is to drill the through-holes with your CNC, then take the part to a drill press which has a drill stop and make the countersinks manually ... unless of course you are manufacturing something in very large quantities, or something that is a regular production part.
Why? If you're countersinking on a CNC it becomes very critical to mount the material flat and horizontally true, otherwise even a small height variance along the part will affect the resulting size of the countersink holes on the part. Even if you mount your part very flat, the burr created by drilling a hole can lift the part just enough to affect the countersinks. While for most screw heads it doesn't really matter if the hole is a bit too big, your, or your customer's eyes can really pick up on the small changes and if you have more then a few countersinks on a part it doesn't look very professional ... or at least that has been my experience .. not sure if this applies to your application.
By the way .... good look with BobCAD V21. I sold my copy right here on this forum to another member for, I think, about 25 cents on the dollar, and I was happy to get rid of it.