I would use a wake on comparator interrupt or pin change with a permanent sleep instead
@ SLEEP

a PIC10F204/206 can wake from a comparator or any pin change, really cheap, would be a perfect choice. Would require only a few lines of code.
http://ww1.microchip.com/downloads/e...Doc/41239D.pdf

Is it mandatory to supply 5V to your PIC? What's the requirement for the Output pulse amplitude?
Why i'm asking, refer to figure 13-2 and later.