We have an admin network set up in our ICT Office here at St Marys and it is unfiltered. We have set up with two cards in our PCs so we can get on our main school domain and the admin name to get around the filtering. Also we have out itcoord@ address as a recorded address with CLEO and LCC so that unblocking requests coming from this address are approved by Smart filter. All it took was a letter from our head teacher to get this sorted, so do not let them fob you off.
Any chance of copy of what your head wrote (sanitised of course). No point in all of us reinventing the wheel. :)