Found this link, seems to do what you want, but I have no experience of it.

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http://minnie.tuhs.org/pipermail/mp3encoder/2002-February/004595.html

Hi Jaroslav,

You could try "WaveMP3" rel. 1.2

Adds/strips a Wave Riff header to/from your MP3 files.

http://home.pi.be/~mk442837/
http://home.pi.be/~mk442837/wavemp3.zip