It Cant Be Done, You Need To Get In Touch With The Other Person To Get Them To Release The Pin So That You Can Use It.......damn that was hard typing out that message lol.
And please dont capitalise every first letter of your word...it looks ridiculous.
It's MUCH easier for the original owner to get the PIN released, but in a pinch your provider can get RIM to do it. You might have to get your call escalated. Be polite but firm, and they MAY give you some **** about having an unsupported BB. Make sure to let them know how much you need their help and how grateful you are, again polite but firm is the key.