hmmmmm first shot, ask later, sorry man!
You can do a request download or an Initial dowload of the BUPA_MAIN, but if the master will be ECC and you want to keep it in sync without triggering from CRM then...I don't know I never faced this requirement in a project.
I just did a quick search on scn and I found lots of information about it, like:
http://scn.sap.com/thread/261124
Please keep us updated now I'm quite curious