I don't thinks there is any correct way to physical distroy part of an IC
 without totaly distorying the device. You could
try charging a up capasitor, and then discharging it into the i/o line.
 Depending on the number of joules you slam into the  output transitors, you may
 just kill them, but on the other hand you may distory the whole chip. In either
 case, it's not
going to be a very reliable method, and would not be suitable for production.
        Have you considered potting you PIC in a lump of eproxi resin, may not b
e very
 suttle, but if you can't get to the lines you need, you can read out the
 code...

Have fun. Mike...