Spreadsheet Voucher Upload

We are wanting to use the delivered spreadsheet voucher upload file for certain vouchers. We ran into an issue, because we need to be able to specify the Supplier Bank Account Sequence Number. (BANK_ACCT_SEQ_NBR) However, this is not available on the current upload file. Nor do I believe it is included in the Voucher Build process. Has anyone ran across this, or found a workaround?