Check this product out.
It's a little button you put by your sink that makes a pump run water through a temp sensor until it hits a specific temperature (I believe its 90 degrees). The water that isn't hot enough is pumped BACK into the water heater so none is wasted. Then, after a few seconds of the pump running, you turn on your faucet and BAM, hot water.
Faster Hot Water From Your Tankless or Storage Water Heater
I haven't tried it as I live in an apartment, but I'm fascinated by the idea.