Think about a Metlund D’Mans or a recirculation system. When you have a wait for hot water, it isn’t because the heater doesn’t have any. It’s because it takes awhile for hot water to travel through the piping to the faucet. Water in the piping cools off when nobody is using hot water.
The Metlund is a pump that you activate by pushing a button and draws hot water through the pipes so you don’t have to run a lot of water down the drain.
I’ll leave it to EnergyExpert to comment on the possibility of installing a second element.