The Prius is of course special when it comes to engine off goodies. It is equipped with electric power steering so no engine needed to have power steering. Shnazzy eh?
Honestly, your best bet is to probably read over this post on cmpg. This is a technique developed by one of the members there and its probably your best shot at good highway mileage. I'll also message one of our resident Prius owners to come say a word.
http://www.cleanmpg.com/forums/showthread.php?t=1224