I recently implemented a workaround for that using the standard Sage 100 A/P ACH functionality. Basically, to be able to instruct certain vendors to hit the client's AMEX, we created a separate Bank Code, we set the Vendors up as Elec Pmt, entered in bogus Elec Pmt credentials for each Vendor because we're not actually paying via ACH plus that info is required for successful ACH processing, created an 'AMEX ACH' UDF in Vendor Maint to flow to the Invoice so that it's easily determinable via Invoice Pmt Selection which invoices are AMEX ACH (because the client needs to do them separately from their true/real ACH's they perform), then perform Check Printing for ACH which e-mails the Vendors the attached customized ACH Remittance upon updating the Check Register (and we don't do anything with the generated ACH file).