Agree with all of the above re the integrity of the OEM hitch solution. The U-Haul design is not even close.
Interestingly, my local U-Haul has a memo from their head office that says they are not allowed to touch an X5. They paid out so many damage claims that they won't go near one now. I only found out because I had the OEM hitch and wiring, and when I rented a trailer they asked about my wiring. When I said that I had the OEM wiring solution they said great, because otherwise we can't help you or rent you a trailer. They were quite willing to talk about their previous experiences. Their modified hitch with the strut running forward was a design modification due to early models bending the X5 rear pan.
For a bike carrier, you are pushing the limits of the OEM hitch. It isn't the tongue load that matters, it is the twisting (bending moment) applied by the CoG of the bike. The hitch is designed for a point load at the hitch ball. A carrier twists the hitch, essentially. Static load calculations would suggest that you may get away with a couple of hundred pounds mounted fairly close, but now add in the dynamic loads (going over a speed bump, for example). Dynamic loads can be multiples of static loads.
Previously discussed here:
http://www.xoutpost.com/bmw-sav-foru...solutions.html
and in many other similar posts. Search on 'bending moment', that is how I found this old post.
Here is the label that comes with the OEM hitch for maximum tongue weight, and more importantly, intended location of that load. Notice that the hitch is designed for the load to be applied (fore and aft) below the hitch centreline. With a carrier, the load will likely be significantly above the hitch centreline, and thus outside of the design limits of the OEM hitch.
Good luck.
Jeff