Managed to get this working - here is what I did for those who may be looking to do the same thing...
# put the disk in a writable mode, as Lee said
$ sudo /root/mount_rw.bash
# stop service
$ sudo service rtlsdr-ogn stop
# remove the current RTL SDR install
$ cd ~/rtl-sdr/build
$ sudo make uninstall
$ cd ~
$ sudo rm -R rtl-sdr
# install new drivers - instructions taken from the OGN google group
$ git clone
https://github.com/rtlsdrblog/rtl-sdr$ cd rtl-sdr
$ mkdir build
$ cd build
$ cmake .. -DCMAKE_INSTALL_PREFIX=/usr -DINSTALL_UDEV_RULES=ON
$ make
$ sudo make install
# I ran into problems with a conflicting file so I renamed it to something else which fixed the problem
$ sudo mv /usr/lib/arm-linux-gnueabihf/librtlsdr.so.0 /usr/lib/arm-linux-gnueabihf/my_librtlsdr.so.0
Then I added BiasTee = 1; in the RF section of the OGN config file located at ~/rtlsdr-ogn/rtlsdr-ogn-paw.conf
# start service
$ sudo service rtlsdr-ogn start
# put the disk in a non-writable mode, as Lee said
$ sudo /root/mount_ro.bash
Then I confirmed the bias tee was working by measuring 4.5V on the SMA connector of the dongle