If I were to use two single handers, this is probably what it would look like. With the marble trackball in between the keyboards I'd probably have to raise it up so it was as high as or higher than the "inside" edge of board(s). To give an idea of scale, in the last piccy the trackball is sitting on three VHS tapes placed vertically.
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(http://i82.photobucket.com/albums/j245/saxeharp/general4/single11.jpg)
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(http://i82.photobucket.com/albums/j245/saxeharp/general4/single12.jpg)
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(http://i82.photobucket.com/albums/j245/saxeharp/general4/single13.jpg)
Joe
Ha, that is great! It looks like you could command the Enterprise with a setup like that.