I came up with a circuit using:
an inductor, cap, diode, and MOSFET driven off the PIC's PWM pin to generate the negative voltage;
a couple of resistors to form a voltage divider so the PIC can take an ADC reading to adjust the PWM period to regulate the neg voltage;
a single digital output to switch on and off the pullup for the voltage divider. This is necessary in case you want to shut off the PWM, otherwise the voltage divider will reverse the voltage on the -vee cap.
A zener diode on the -vee in case your code fails to regulate -vee properly.
It's not too complicated, but it does tie up several good PIC resources. The great thing is you have full digital control over contrast inside the PIC without an exotic external component. So you don't have to mount a user-accessible contrast knob, which is a huge pain in the ass. I have another ADC pin reading a thermistor and automatically adjust the LCD contrast based on temp. This is also VERY useful if you put it in a car or anyplace where the temp can vary a lot. Twenty deg will make a display disappear or turn all black without a contrast adjustment.