To add the bridge pup to the neck in position 5, run a wire from lug #1 on your 5 way switch (where the bridge pup is connecte) to the middle lug of your p/p. Run a wire from the top lug of the p/p (the one that connects to the middle lug when the switch is pulled up) to the lug #3 on your 5 way (where the neck pup is connected.
When your p/p is down, you get normal pup switching (b, b+m, m, m+n, n). When the p/p is up, you will add the bridge pup to the neck pup in switch position 5 (normally neck only).