These are all interesting approaches. Thanks. I'll give them a try.
Pat, I had considered your technique, and I think it will give me the closet results to what I want.
Kevin and Ken, Imagine how this is made in real life. The frame is assembled, and then the router with a piloted round over bit is guided on the inside edge of the frame, and the router base rides n the top face of the face frame. The inside corners get shaped like Ken's example, but the they are square on the flat inside edges like Kevin's example.
Ray, I like what you did there! It's kind of what Pat was suggesting. The way you handled the end of the fillet cut is nice. It may not be exactly how the router would do it, but it certainly is close enough. I also like your "Custom Selections" palette. I will mess with that a bit too.