With the exact same starting territories
One option is same person plays same starting squares
Other option is to swap over

I assume but have not tried doing custom scenario could be used ?

Is there an easier way or an easy way in custom scenario

As far as I know, custom scenario is the only way, but its pretty easy to use.

Head to custom distribution, and select all the territories for each slot, set them to the right amount of starting armies, add wastelands, and then you can save this template and switch between slots afterwards.