Completed the installation of the SSK on my 2008 E90 335xi tonight.
The bad news is there is practically no way to access the clip from below the car. The good news is you don't have to get under the car.
First of all what I found on the xi was not quite like the install that started this thread. There are no pieces of foam, carpet, etc that need to be removed. The aluminum bracket for the ball and cup are very different, spherical shaped, with access only from the drivers side.
The biggest finding, you can install the clip with a needle nose pliers through the ball/cup opening before you snap the cup in place. What I don't know is if you can remove the clip from the stock shifter that way because by the time I figured this out I had removed the entire console. If you can remove the clip through the same opening this would be a 30 minute install at most.
The stock vs short shifter are very close to the same overall length, only the pivot ball location is different which changes the leverage ratios. I installed the shifter with it tipped toward the back of the car as when I layed the stock and short shifter together the angles matched almost perfectly that way.
Use some spray silicone inside the rubber boot to slip it over the new shifter, glides right on.
I also installed the M shift knob so I can't say how much difference just the shifter makes but I can say together it is a huge improvement. It definitely got rid of the "I'm shifting a farm truck" feeling.
Install was kind of a bitch since I was in exploration mode but if it is possible to remove the clip without removing the console this would be a very easy install. The next person who tries it will have to answer that question.
I have a lot of pics but I will just post a couple tonight.