Most likely is the floor pan; since you are a geek (I'm a retired geek) you've probably seen the batteries in the tablets, they can be just about any shape and size now. The electric could kick in at highway speed, just like the new GM and Chrysler motors go down to 1/2 the cylinders.With current battery tech and the limited volume in an Elio I doubt an all electric Elio would have an acceptable range. I drive about 84 miles for a round trip commute.
Hybrid might work, but for my commute I'd probably end up using gas more than electric. So the added weight and complexity of the hybrid parts would be wasted.
The new Tesla 3 <see below> has that setup (battery is the floor pan), along with the BMW i8, the electric motor could share room under the hood (you might have to stretch it a bit) that would connect into the existing tranny. But I doubt the Elio could be battery only and carry enough storage to give it any kind of long distance range. The 10 pounds of stuff in a 2 pound bag dilemma.