Mediaportal will not allow this with it's current setup.
The far more sophiticated PVR-Scheduler may even have trouble doing this, but have a look at its options, this is the website address.
http://www.pvr-scheduler.de/index.php
It's not officially a part of MP, but stsc does a good job of incorporating just about anything, with scheduling different power options.
If that will not do what you want, then nothing will that i know of.