I assume the PIC pin joining the 12F683 to the junction of the 10k, 2k2 and 100nF is the PWM out of the PIC.

What you need from the PIC HPWM is a series resistor - say 1K, then a large cap to ground, say 100 uF. This time constant is 100 mSecs so the HPWM frequency should be at least 1 kHz. The junction of the 1k/100uF then goes to the ground pin on the regulator.

HTH
Brian