You don't get any sort of notification (even via ProntoScript) that the screen is activating. Something like you are requesting might be able to be done but it is NOT easy and might be plagued with timing problems.
Unfortunately, you did not provide enough information about your use case such that we (Barry and or me) could formulate in our minds whether or not we can see a way to make this happen.
Don't get your hopes up. Unless you can come back with additional info, I'd say scrap the idea because the implementation that Barry and I would use could easily break if the firmware was changed/updated by Philips in future revision.
That is, we rely on specific behavior of firmware "today" to detect certain things. This could change in the future. (A very technical discussion about when Javascript actually runs on the remote and how we detect when remote is actually asleep and is then waking up which involves use of scheduleAfter() and or repeating pages).
