Yes, there are a very few FAA approved "agents" operating in Europe (or at least I assume they still are) who will do the honours for a fee not too far removed from the cost of a trip State side. I doubt unless things have changed their service saves money but it does save time.
Hopefully some one else can provide you with more specific details.
Strictly I am not sure it is correct to say "ratings are automatically added", more the case that you are entitled to excercise the priviliges of your CAA / JAR / EASA license, so for example if you have a night rating you can fly at night, but without, even though you would be entitled to fly at night under a stand alone FAA certificate, under a 61.75 you have no night priviliges. The IR as you correctly point out is the exception as is there some debate regarding type restrictions in Euroland licences which are not restricted in equivalent terms in FAA land.
Bookie has some interesting views on this topic with which I agree.