Hey Joe!
It sounds like you'd be interested in a CAN Logger. I'm not sure if there are any that interface specifically with the BMW CAN Bus system, but try a search on the net and see what you can come up with.
Here are a few to check out. Try giving the companies a call during the week. All pulled from google.
https://www.vector.com/vi_cancase_xl_log_en.html
http://www.kvaser.com/en/products/can/data-logger.html
http://sine.ni.com/nips/cds/view/p/lang/en/nid/209237
http://www.intproducts.com/unicanlogger.html
Hopefully this thread will kick some interest on development.