I've been thinking of a home-brewed hybrid electric vehicle
 

Let's say we use my 1980 Toyota 4x4 as a starting point. First, yank out the existing engine and replace it with something smaller. Say, a 1.3 liter 4-cylinder from a Suzuki Swift. Take an electric motor (the kind that would normally bolt to the transmission in an electric car conversion) and fab up some beefy brackets to attach it to the side of the engine. Adapt a belt drive from a 12-71 supercharger or something similar to get the power from the motor to the engine. Use about a 2.5:1 reduction since the motor revs substantially higher than the engine ever will.

For the most part, the rest of the install is rather like a conventional electric vehicle conversion. The batteries would be mounted under the bed. The gas pedal would operate both the throttle on the engine and the controller for the motor. You could vary the amount of assist the motor provides by means of a simple adjustable lever - move the input point (the spot where the throttle cable attaches) closer to the pivot point of the controller to increase the load on the motor, move it away to decrease it. You could even have an in-cab adjustment for on-the-fly changes. More assist around town, less assist on the highway.

There is the problem about idling. In a conventional electric vehicle conversion, the motor comes to a complete stop when the vehicle does. This wouldn't happen in this case, since there's a belt between the motor and the engine. The motor will keep turning when the engine is idling, like at a stoplight for example. I see three potential solutions: 1) The engine will simply be strong enough to turn the motor while idling. 2) You could feed the motor just enough electricity to eliminate the load on the engine. 3) Have some kind of engine-stop feature like production hybrids do. When you step on the gas pedal, the motor turns the engine over and it begins running again. #3 would be pretty easy to implement, and I think would be the most elegant solution to the problem.

What do you think?

or you could modify a clutch to disengage the engine from the electric motor. this is probably not a good idea since i don't want to take the time think it completely through

The clutch from a Festiva is pretty compact and would be strong enough. You'd need a way to actuate it. Maybe some kind of link to the clutch pedal, so the pedal operates both clutches. Hmm.

could you modify the brakes to work the clutch as you hit the brake completely the clutch disengages the electric

You won't necessarily want the motor to disengage while braking. When the vehicle is coasting, the unloaded motor will be an added drag, slowing the vehicle further. This could in fact be beneficial - think of engine braking while going downhill. This lessens the load on the brakes, which is usually a good thing.