Hmm, you probably want to make some sort of private variable, say a Boolean named "Active" that you set when the object is clicked on and then when the mouse is clicked again you select the object with the "Active" bit set to True and make it move towards where the mouse is. When you click an object you just set the "Active" to false for all objects and again to true for the one that was clicked on.
There may be a more efficient way, but this is what comes to mind.
PS. Forgot to mention - there's currently a critical bug in the latest (r66) C2 that crashes if you work with private variables so if you haven't installed yet you are good to go or, if you have - tough luck.