Hi James
It can be done in SAP but requires custom work. It is probably not worth the effort when you have PI available. I did it in the past (we didn't have PI).
I created custom IDOC with one custom field added, this is the filtered field for ALE model to route the IDOC. One IDOC to one partner.
I created one output type per partner we needed to route the IDOC to. It was complicated in it's own right to set these up so they were all available to be triggered from every document created.
Custom code in user exit for save document triggered each output type in succession, populating the custom field for the ALE model to use for routing.
In short, duplicating the IDOC was the only way I found to leverage SAP standard functionality.
I also set up a purge job for these IDOCs to delete them after a week. They were around long enough for any troubleshooting, then purged. The IDOCs themselves were unimportant for us and this helped keep the database clean.
~~Sue Morton