Edit: >_< I read 'radio knob' and totally missed the part about volume. I'm not sure about anything for that, but station changing...
http://www.fallout3nexus.com/downloads/file.php?id=4709 lets you switch stations. Incidentally, FOOK2 will be including that excellent mod in its next iteration, v1.1, and will also hopefully be able to have a new way of turning the radio ...http://www.fallout3nexus.com/downloads/file.php?id=4783. ^___^
I might be able to rig the FOOK version to have a volume option by raising/lowering the Z coordinates of the source of the radio sound (an invisible old man). I'll tinker with it and post the results later.
*if FritZ FretZ is game