Hi Charles,
I'm jumping into this discussion a little late but I had a very similar issue with the 635 style spoiler that I bought from CoupeGuy. When I received it, I thought there was no way in the world it would fit, like yours it was way wider than my car. Dan told me the same thing that he told you. After a lot of modifications (mainly to fit the bumper), I made it fit. It loses some if it width as you wrap it around the front to car but it takes for ever to get it right. I have a ton of hours in my air dam, I can't tell you how many times I had to test fit it which means placing the bumper each time. I love the way it looks so it was worth it, plus I did years ago so I have forgotten most of the pain.
Here's a write I did a few years ago. Dan sent me a very nasty PM when I posted it.
http://www.e9coupe.com/forum/showthread.php?t=7137