I never did it, but I think It could work. Use a pull up between tr base and 12V, then a resistor in serie with the PIC. In your software, you set GPIO to 0, and later you play with TRIS to toggle your pin. Set to input, the tr should be off, Set to Output, tr should be almost ON. I would bet something like 10K pull-up, and something like 100-1K match could do.