I've actually taken a look at the ACR cutouts... and they have no trim ring at all...just a nice razor clean cutout similar to the pics of Andy's work.
The only trim ring that would actually look authentic that I have seen, are the ones that most child safety seats use to allow the belts to smoothly slide from the back of the seat, but unfortunately, in all that I've seen (and with 3 kids I've seen quite a few) they all are narrower than your adult width harness...but the installation would literally be a snap (as they are all made to pop out so the upholstered cushion can be washed).
You might want to check out your local K-mart, etc and see if any of these trim rings are actually of a width that would accomodate, and I'm sure you'd be able to call the manufacturer and get 'em quick.
Good Luck! Let us know if you find any suitable.