the 1st and 2nd page of this thread has some pics of the support.

http://www.xoutpost.com/x5-e53-forum/...-x5-hitch.html

But since the OEM hitch is (or will be) available, it is probably not worth it to make mods. If you don't want to risk it or tow heavy loads - get the oem.
If you tow under-capacity, and don't have a huge tongue load, the curt will probably work.