Hi Pradeep,
I understand your concerns. Unfortunately I'm not an ALE expert, so I can't say, whether the FILE port can be customized or modified or whether there are any other "user exits" in the ALE layer that can be used to achieve your requirement. Something like that would of course be the easier solution for you.
(However: SAP BC is not "another sap system"... It's only a small component that can be installed in 10min. Perhaps you can try it out in a test system as a proof of concept and then decide, whether it would be too much effort for your client or not?!)
Best Regards, Ulrich