by Simon Heissler.
i understand what you want but I wonder why it is necessary. In the email they get there is just information that a assignment is graded. When the student opens up the assignment the feedback is presented just beside the grade. I suppose they are as interested in the feedback as in the grade?
If you want to force them to read the feedback you could greate a scale which you use for a two step grading: failed/feedback given/passed. When submitted you grade with "feedback given" - this returns the assigmnent to the student and he/she has to submit a second time including answering your feedback. Then you grade with passed...