To be clear: think of your ESC as a electrical gate; the on and off and partial throttle is making it working hard, the ripple current is the killer, that's why you see extra capacitiors on some ESC. People also install what they call 'cap bank" for this reason. So the only alternative way of gaining more run time is to get higher capacity batteries and running a smaller prop. Smaller prop usually is used when a slower speed is desired in testing rather than using part throttle.