There are a ton of free programs that will do batch conversion, including batch conversion from WAV to OGG. Use Google. Really.
However, just stripping the sound/music (or anything else) straight from a commercial game is
definitely illegal. And it's rather silly to do that for a KS level!
You can use remixes.
Remixing such a song is even more illegal than putting it in a KS level, and putting a remix of such a song in a KS level is about the same level of illegal-ness as putting the song itself. Okay, so that sentence was probably pretty hard to comprehend.
However, I believe this thread is about WAV support, on account of, you know, the thread title. It would be laughably easy to implement, but WAV FILES ARE ENORMOUS; not going to happen.