>We were trying to get mist to pour out of my middle tenor, but we never found a good way to make that one happen.<

You MIGHT be able to make that work with an "electric cigarette". The ones I smoke have a flow vale, so they only produce their "smoke" (wich is really just water vapor) when there's airflow through them. If one was stuck in the end of the chanter, it SHOULD produce a small cloud of vapor when the pipe is playing.

Of course, it would also mute whichever drone it was in...