For those of you unfamiliar with Back To The Future folklore, there was a trilogy, and it was good, even with that idiot, Doc mucking things up...
Anyways, I always thought that Doc Brown was an idiot, with the exception of the flux capacitor which after all, is what makes time travel possible.
It was in Back to The Future III, where Doc really screwed things up and got himself stuck in 1885. I mean he clearly couldn't even figure out how to get the DeLorean up to 88 MPH without any gas... Well, in the movie, they decided to push it with a train... I know right? Totally unrealistic...
Doc, you are an idiot! The answer is simple and it was discovered hundreds of years ago by a guy named Newton, Isaac Newton... maybe you've heard of him. It's called gravity... duh!
It's simple, with the Delorean missing it's fuel injection manifold that YOU blew up trying to make your own gas and without any way of fixing it, the easiest and best solution is to drop the DeLorean. That's right, I said drop the DeLorean. Did I just blow your mind Doc? I bet I did and I didn't need to bust my head open on a toilet to come up with it either!
The speed of terminal velocity for a skydiver is 124 MPH. The hot air balloon was invented in the 18th century, long before Hill Valley was even on the map.
As I clearly have illustrated above, once you drop the DeLorean, it would quickly reach 88MPH sending Marty AND You back to 1985, where once your parachute deploys, you will safely land and leave the whiny school marm Clara back in 1885 where she belongs.
Your welcome "Doc".
Your friend in time,
Doug A. Cox