How about splitting picking code into two stages:
1. You do checking to see if your mouse is over selectorblock (only checking those sphere that are used for detecting selecboxes. If your mouse is over selectorblock you end here else you go to second stage. In order to achieve better optimizatio you may add aditional logic check to see if secetor block colision is even needed (depending on your editor implementation you probably won't need this at all times) if not you simply skip to second stage.
2. Here you do checking to see above which map cell is your mouse.