I use getting in an out of the car as a start, just like you.
I also use every chance I get when out and about.
Crossing a fallen log, give the command.
The pup isn't really jumping, more scrambling at this stage.
I wouldn't be in to much of a rush to teach jumpimg as you can use a fence to your advantage later on in steadying up the dog to dummies.
That said I've a 10month cocker that is now going over 6ft walls!!! Cant stop the mad thing, she loves it