To be useful to someone else, I answer my question. I did to set the sensor mouse overfor each object inside the scene and add a python script controller to set the property of the scene Empty object.
import GameLogic
import Rasterizer as r
r.showMouse(1)
print 'SetProperty.py\n'
cont=GameLogic.getCurrentController()
obj=cont.getOwner()
emptyOb = GameLogic.getCurrentScene().getObjectList()["OBEmpty"]
emptyOb.EmptyProp=obj
print 'object name, within emptyProp: ', emptyOb.EmptyProp
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