I received a Nyko Wii Charge Station for Christmas, and finally got around to hooking it up and whatnot today. I had previously been using batteries out of my Wavebird in my Wii remote, so when I went to put the battery pack in the Wii remote, I put the batteries back in my Wavebird. Upon doing so, I noticed that the shape and layout of the Wavebird and Wii remote battery slots were identical. Being of the curious nature that I am, I tried putting the Nyko battery pack in the Wavebird, and it fit! Then I tried turning it on and using it, and it worked!
You can't put the battery cover back on the Wavebird with the battery pack inside, and I don't know how useful it would be, but just figured I'd share that little tidbit.