business rules & automatic assignment of a template

Hi.

some of our users send their service requests via email to an account which is fetched by SD+.
We have set up business rules in order to fill out some fields.

How can I automatically assign a request template (including tasks) to those calls?

As an example, lets say that user XY usually sends an email with the subject "SUBJECT" to the SD+ helpdesk account:

a new incident is created automatically (via mailfetching) and
some fields like urgency, impact, priority, request type, cat, subcat are filled in according a business ruleset (if user=XY and subject=SUBJECT).
The only thing that is missing now, is to AUTOMATICALLY assign a pre-defined request template with tasks to this request. How will this be possible? Manually, it can be done by editing the incident and changing the request template.

Thanks a lot