It's probably a lot easier to start with a hybrid, but I betcha there are at least some attempts over at DIY Electric Car forums to poke thru, or on EVAlbum, to see how anything that's already been tried turned out. I think there are also some here on ES, but I don't think they went past the thought stages.
I recall a discussion somewhere about replacing the serpentine belt system on a regular car with a heavy-duty chain and sprocket system, and then putting the electric motor in there along with the other stuff in the drive path of the chain. Then it could be used as a generator to charge batteries with whle the ICE is running, and could be used to drive the crankshaft of the ICE (and thus the transmission) as a motor. But that method means it also drives the ICE itself, pistons/etc., so you'd need something that keeps it from working hte fuel system and wasting fuel like that (and it'll still waste electric power). I think the original intent for the thread I saw about it was simply to add more HP to the existing engine, for hills and quicker acceleration.
A better but similar setup would be to input the electric into a coupler between the transmission input and ICE output, but that would also require a lot of mechanical changes in the car itself to move the ICE forward enough for that, and for placment of the motor, etc. And you're still left with no accesories, if htey are powered by the belt on the ICE. So fi you need A/C, power steering, etc., you'd need to get electric versions of those if you don't have them already.
Hub motors would be a simpler system to engineer from that standpoint, but they add unsprung weight to each wheel they're in.
A push-trailer is another possibility, cuz you could put all the electrics in it (motor, generator for range, batteries, etc) if you wanted, and simply put it on any car/truck. But I doubt it would drive the way you expect it to when being pushed by the trailer, instead of pulling it, and you'd probably need a hitch designed for the purpose instead of hte regular ball hitch (depending on how well a normal ball hitch could hold against pushing instead of pulling). That's already been done a few times; I've seen documentation and videos on the web here and there.