[aerohead]

If I were tasked with getting an Odyssey up to 32 mpg I'd go right for the tail.
Your Cd is 0.32,and to get to 32 mpg would require Cd 0.19.You'll never get there without putting the wake on a diet.
If she were mine,I'd remove the rear hatch and construct a clamshell-door,or swing-away boat tail.
You'll compensate for some of the weight of the new tail by removal of the hatch,and you'll have an opening tail for loading and unloading.
Cargo aircraft will give you some ideas for how to articulate things.
My femmebot has an Odyssey and Honda's done a good enough job with it to go directly to the tail.
The other mods will be table scraps compared to this main course.