Thanks for the replies - it helped me get through the "Block"
I finally decided to create a .txt Text Document Template that has the structure of the .ics file. This file contains Tags that are replaced by an instance of a Appointment object that is in context.
I the export this file as .ics and import it again into an Attachment Attribute defined in the Notification that is sent out as eMail.
This is most probably not the most elegant solution, but I prefer having all the document and object definitions defined and managed within the BSV.