[seabass-labrax]

Which pipes are these, out of interest?

As for electronic control, it shouldn't be too hard - perhaps you already know the following, but I'll write it here in case it's useful. You'll need as many electromagnetic solenoids as you have pipes. First you need to construct a 'wind chest', which is a shallow, air-tight box that can be made of any material. A plastic storage tub should do fine. Then you punch a hole in the top of the wind chest for each pipe, and make some sort of grommet to hold the pipes in place in the holes; this would be a 'toe board' on a real pipe organ. Mount the solenoids directly under the holes, and attach something soft to squish up against the pipe and stop the airflow. You of course need to have a blower that can pressurise the wind chest.

No guarantees about how that's going to sound! :) If you wanted to construct something really high-quality, you could follow Raphi Giangiulio, who has documented every stage of his fully-mechanical tracker organ: http://www.rwgiangiulio.com/index.htm