Hmm...
Ever thought about a thermostatic shower valve?

Have you tried increasing the temperature setting? If you mix more cold water into the shower, then you'll use the ultra-hot water at a slower rate. Not sure if this is actually a solution to your problem.

It seems that you have an issue with one or both burners not kicking in early enough. They eventually do, but I think you need to lessen the time it takes them to turn on.