This is the exact case with the Prius too (I own one and have the most popular mypermiling
vid on youtube) I'm ordering my Imiev in two weeks.
So, here is my answer. To make it easier to hold your foot in the no-regen spot, It would be
really cool to have a soft detent spot there (in the pedal travel). This can be accomplished by mechanical means.
Alternately, a tactile vibrational feedback on the pedal would be perfect. It would softly vibrate right at that position.
This would be accomplished by using IR LED sensors and a Cell phone vibration motor. That's safer than a mechanical system.
You don't have to look at the gauge and it trains your muscle memory as to where the sweet spot it.
Regen is useful over a certain angle of decline on the road. That's the spot where regen doesn't slow you down.
An indicator to show you what that angle is- would be comprised of a two-axis accelerometer and either
schmidt trigger comparator or a full-on microcontroller driving LED's. It's actually a simple project.
It's really that no battery chemistry can efficiently take a charge in such a short time. Ideally, this would be handled
by super-caps. I have no idea why nobody has done this.
I'll be showing plans for a Level 1 solar charging system and and elegant rear-end collision avoidance system in the next 4 months.
The above items may find their way here too.
I'm getting excited!