Physically it will fit, the only realy problem I can see will be a playability issue. If the 1P buttons are right aboe the trackball it will make it difficult to use them when you're playing tracball games, unless you're going to map all your button requrements on to the 2P buttons, since I believe that most of the trackball games have the buttons to the left side of the trackball.
Just something to think about.