How do you handle customer numbers for different entities?

My client will have several different AP Business Units for facilities that currently have unique customer numbers for a particular Vendor/Supplier.  This helps the Vendor/Supplier determine where to apply cash for payments.  It appears that PeopleSoft only supports one number per Supplier.  I could setup different Vendor Locations, but I would have to use one of the Additional ID Number fields.  By doing that, the user would have to select the correct Location when creating PO's or Vouchers.  Does anybody have a better idea?

Thanks,