relay could be used... some reed relay are small and don't need many current.

BUT you can also use transistor (PNP) or a MOSFET (P-Channel) to do the same thing. What is the current needed by the whole i/o PIC with all component attach to?

OR you can also use the MCLR pin on the I/O PIC. By sending a high level to this pin, your program will run and while holding it to ground, it will stop....