In 2005 Alex Loscos & Thomas Aussenac, created WahWactor, a VST plugin that lets you control a wah-wah filter through a voice signal.
From the abstract:
Using a wah-wah pedal guitar is something guitar players have to learn. Recently, more intuitive ways to control such effect have been proposed. In this direction, the Wahwactor system controls a wah-wah transformation in real-time using the guitar player’s voice, more precisely, using the performer [wa-wa] utterances. To come up with this system, different vocal features derived from spectral analysis have been studied as candidates for being used as control parameters.
Visit the WahWactor page for more information and a link to download Wahwactor VST plug-in v0.2.