Yes, the internet can be a wonderful thing. One of the disadvantages of using the female template with different diameter bushings is that with a large bushing and a not so large radius cut in the template, you can wind up with a short arc and not a quarter circle. To the extreme end, say a 1" radius in the template and a 1 1/8" bushing, there will be no radius at all except that of the cutter itself.
The disadvantage to the template I suggested for Aaron's job is that with large bits and deep cuts, the router can get away from the operator if he is not experienced. With his little veining bit and shallow cut that won't be a problem.
I put up a series of 3 videos on the video index page of my website on drawing, making a jig for, and cutting elipses the easy way with a router, virtually infallable.
I used to do a lot of eliptical cased openings and it was easier for me to simply make the casings too instead of having to sub it out, then hope they were correct. I had to do the framing and jambs anyhow.
In making the casings, I discovered that there is no such creature as concentric elipses. You can make them close - but no bannana. I had an idea of how to modify the jig to get the outside cut very, very close with the router on one shot , but never got around to doing it.
The videos will, however, show how to cut forms for both the jamb and inside edge of the casing. I never got around to showing how I do the outside edge. Life keeps happening to me.