First a plug for the best Sleep text by far, "Principles and Practice of Sleep Medicine", by Kryger, Roth, and Dement. If you don't have this, you need it.

To turn off the circadian alerting, it would suffice to suppress cortisol.

I would think that there is plenty of low hanging fruit to exploit before that though. After well known sleep hygiene measures have been addressed, and pathologies excluded, the largest remaining drain on sleep quality is maladaptive emotional processing. See Barry Krakow's "Sound Sleep, Sound Mind" for lots of detail on this. This book is rather unusual in making a big deal of the link between poor emotional processing and poor sleep quality, but dude is a very highly regarded sleep specialist who had been running a top-notch sleep clinic for many, many years, and not to be pooh-poohed lightly.