I'm afraid multiple actions are not supported here.
I guess I could change that in one of the future versions of the program... but honestly, the boot-time scan has never been meant as a regular (or even scheduled) scanning method (but rather something used for cleanup when an infection has already slipped through). Yes, the boot-time scan may be able to see (and act) deeper by starting early - but on the other hand, it doesn't have network access so it can't use any backend services (which Avast, as well as other AVs, use more and more).
When scheduling from the UI, this limitation is partially rectified by offering to download an additional set of virus signatures - but that won't happen when scheduling over sched.exe.