Apparently you can use e channeliser to do this.. ...but I have never done it myself or some providers will give you a script to import to the box via putty which sorts this for you automatically. Maybe ask your provider if they have a script
There is another forum that this is available on.
I know I'm one of the major contributors to the scripts involved. But seeing as it would be an advertisement for me to link to I can't possibly put a link up.