Quite to hijack the topic
here is my announcement of a toolset which can accomplish the same (or a similar) goal; which is, mine only when the computer is not in use:https://bitcointalk.org/index.php?topic=265232.0
Note that this toolset can enable mining whether users are logged in or not (at bootup *and* after users log on and off).
At this writing it can only alter the commands (for example to run miners with different settings during the day vs. night) by altering the command text files. It may in the future be made to automatically run configurable (for example possibly alternate) commands upon user resume from activity, and/or on a configurable schedule.