PeopleSoft Billing integration with Coupa/Ariba/etc

More clients are requesting invoicing to occur via their Coupa/Ariba/etc Portals and are asking for the Invoice PDF plus some enriched data be loaded. As far as I know PeopleSoft Billing does not have integrations with these packages.
How have others dealt with this. I have seen this done at a previous company by developing an external tool that integrates with PeopleSoft however we are looking to see if there are alternatives to that.