Perhaps one of the reasons I'm so "grinchy" is because I've been holding my breath for so long waiting for permission to edit the bloody FAQ that was...
My advice would to be wait until 9.1 comes out, there are going to be a lot of MAJOR changes to the jail system and none of this might be necessary....
if you have no control of the router, then no, there is nothing you can do. that is the purpose of a NAT device, to essentially firewall off devices...