Ok, I got Bluetooth pan working on the n9.

Just remove network from the DisabledPlugins section in /etc/bluetooth/main.conf .

After that I got pan working with the test-nap.py script from the bluez repo and the tether.sh script from another thread on maemo.org.

I have put all the files into this gist: https://gist.github.com/4133214

The last missing bit is ipt_MASQUARADE but as workaround we can use BlueVPN in conjunction with pan networking to workaround the Android online checks and the missing ipt_MASQUARADE on the N9.

Fully working Tether Nexus 7 <--> N9