Add converting lamps from 1-way to 3-way as a skill I didn't know I had. But really, it's simple, with the hardest part removing the existing socket from the screw post. Only costs a couple bucks for the new socket.
Look closely at the sockets in the picture below. The socket on the left is a 1-way switch, the one on the right the 3-way. The 3-way has a silver tab on the black tab at the bottom, and that's the extra connection that's needed. The 3-way bulb will have a matching connections. Those two connections allow for the three levels of light.