Prius has built in drafting mode!
 

"Dynamic Radar Cruise Control
The available Dynamic Radar Cruise Control System (DRCC) 24 automatically adjusts vehicle speed to maintain a preset following distance between your Prius and the vehicle traveling directly in front of you."

Hot damn!

I suspect the preset distance is beyond that of a draft.

Besides, if the car ahead of you is constantly changing speeds, this will likely hurt your mileage,

The Fusion hybrid does have an Eco Cruise that reduces the throttle inputs. So the system doesn't go full throttle when the speed drops 2mph.

I'd say there's a good chance that the distance is appropriate for the only kind of drafting that's useful for FE, a 2-3 second draft (further than most people follow when not drafting) behind a 53 foot box trailer.

Which is what I had in mind. :)

Which is the recommended safe distance. Even behind a semi, you still have to consider the drawbacks of cruise control on hilly roads and varying traffic speeds.

Should point out that many cars have adaptive cruise control now. Not just the hybrids.