Never built it, but I had an idea for a starter "clean box" not to long ago. The plan was to take a clear plastic bin. Cut a whole in it and stick a computer fan or any small fan at one end so that it will suck air out of the box, then cut another whole and put one or more of those sanitary air filters in the other end. when you put your starter in the box you'd turn on the fan which would suck out old air and replace it with the sanitized air. You could cut a third hole to allow the plug of your stir plate to get out of the bin.
I think this is a cool idea, but I thought it was overkill since I have never had any problems with starter in the past.