There technically is no way to make it start only in neutral. On manual cars you have to have power locks. You have to go through this cycle I activate it BEFORE leaving your car. You have to put it in neutral activate it, lock your car and walk away. If anyone unlocks it or opens it it deactivates it and you won't be able to remote start it.
I looked at this before the winter and decided its not worth it. The jeep has so much low end torque that unlike a car, it won't stall out just by going up a good hill. It'll just idle up the hill and only stop when it hits something solid like another car, tree, house, or drives right out into a street and causes an accident. I didn't want to be liable for any of those so I didn't do it.
I'd suggest seat heaters instead if you want to warm up quicker in the morning. Then at least your butt and back is warm while your jeep warms up