If you are getting the event with your method, then I would say that your approach is correct. Triggering an event and/or workflow through change document configuration (SWEC) is completely valid option.
Another option could be finding a user-exit / BADI / enhancement stop and then from there trigger the event via SAP_WAPI_CREATE_EVENT function. Requires of course a bit of coding.
A bit strange thing is that if the standard doesn't trigger the Released event when the PO is released, when is it then triggered? Are you missing some needed configuration for the PO releasing stuff in SPRO? Probably not (I am just speculating), but just make sure that the Released event is not getting triggered by standard in some other situation and thus making your current solution invalid.
Kind regards,
Karri