If you really want to make the supply voltage lower, just string some rectifier diodes in series (1+A diodes). Each diode will drop the voltage by about 0.6 volts without wasting energy like a resistor would. It's also a consistent voltage regardless of load, unlike a resistor drop solution.
That's a better solution! Didn't think of diodes. You could also use a properly rated zener diode, or LEDs, so that you wouldn't have to have as many in series (both of which have larger voltage drops than silicon diodes).