Okay, you really need to do this with extended notifications. Not only does it make more sense but I guess you will encounter similar business requirements which can easily be fulfilled with extended notifications.
In swnconfig for your own category copy class CL_SWN_NOTIF_WORKFLOW to a custom class and use that one in configuration.
In the class you can do most of your stuff in the GET_BODY method.
I really urge you to go this solid futureproof route, there is a time for fixing stuff with dodgy sticky tape. This is not that time.
Kind regards, Rob dielemans