I have lots of these challenges for my daily drive in my HCH.
First, I make sure that I'm going a pretty good speed as the hill begins. I might take 2-3 miles or more to gradually increase my speed to the base.
Basically speaking, I let her slow down on the way up.
Before I begin the hill I'll decide the minimum speed required at the top. Often times the current traffic condition plays a big part in that decision.
You'll also notice that the hill(s) are not linear to the top: they usually have level or more level areas on the way up. These areas do not require as much fuel as the hill itself and you can save a little more on these areas by backing off a bit.
Since this is your daily commute you know the road very well and can plan far in advance.
In my commute I have a set of staircased very long, steep hills. These are paticularly problematic because there is a light that almost always requires a stop before the hills begin.
The staircase begins just on the other side of the light so there is no chance for a long, gradual period of momentum building.
These are in the first quarter of my 46 mile commute and still have ~20 miles to go before getting any real downhill relief.
I'll begin with a fair amount of accelleration from the light * until I reach the base of the hill, then I'll conserve what I've just burned and keep momentum by backing off just enough to maintain speed up the hill.
At this point I'm still well below my desired speed so on the following more level area I'll increase speed again and go back to the astrisk * (above).
I'll increase speed on the level areas until the desired speed is achieved.
I'll also be certain that the AC is not running during these taxing events.
This technique has worked well in both my HCH and Grand Caravan and surely would at least give it a try in your Prius and see what it does.
