My client has a scenario where paymens made for company codes x, y, z are actually being processed out of a bank account in company code "a". Therefore in order to record payments in company code x, y, z through the system, we've set up the same accounts in all these company codes. We process payments out these individual company codes, but when the bank feed comes back it only applies to company code "a" and you accomplish it by defining one real account in company code "a" and then setting up identical accounts in companies x, y, z but defining them as Alternative account numbers (T012K- BNKN2).
Sounds like the above scenario could be the similiar.