You would need to divert internal line that runs along the piezo elements (which are used for cooling the components) to some other loop with a cooling liquid.
On the nozzle side you would need to do modifications to add a heater, use heat compatible springs etc. If you can only localize your heat to the tip of the nozzle you could get away with using a standard injector. Maybe cool the fuel a lot so it cools the components above and make a sharper heat transition zone.
My idea is that if you have enough pressure on the fuel, then you can heat it up to the temperature you want and when you spray it it will instantly vaporize. You can control the amount injected with the injector.