variable subject and an attachment in an email

I know you can use a mailpackage for defining parameters of an email (like subject, to, from, etc...). It is also possible to email a attachment with the MessageTransformBean in the modules tab of the communication channel (content conversion). Now I want to combine those two features. So I would like to create a variable subject (for example with ordernumber in it, a field out of the original file) and the original file needs to be mapped to a flatfile attachment.

I think I cannot use the mailpackage, because the content of the destination message is being lost then. Does anybody have any idea? In fact I need two mappings on the same interface (1 to construct the email and 2 to map the message).