The only way to bypass that would either be via proxy sites (which could be blocked also) or by changing the router around (which could be done via a voluntary MAC address lock on the modem).
I find that often porn filters cause more problems than they solve. For example I went to do some IT support for a small company in their office, they companied that they were having trouble accessing a whole bunch of sites that they needed for work because they were being blocked.
In the end I just asked the office manager if he though that his staff would be likely to sit around watching porn in the office if I turned it off. Of course that was not a real problem that actually was likely to exist so I just turned it off and improved their IT experience in one go.