How to create attachment with email through partner manager

sorry if this is a common question, but…i haven’t a solution.
I want to send some message content as attachment to a mail. When using pub.client:smtp, its quite simple - but i dont want to create a flow for each customer.
So, the use of the partner manager is probably the way to go. but when invoking wm.PartnerMgr.gateway.transport.EmailTransport:OutboundProcess,
there is no way to attach a file. How can I create one beforehand and apply easily to the mail? Is pub.mime:createMimeData maybe the way to go?
Environment ist SAP BC 4.6
Thx and cheers