SiliconFile Shows How to Save BSI Sensor Area

Siliconfile patent application US20110156113 is nice and simple: let's use higher metals to place capacitors in the BSI array area (notwithstanding the typo in cap name):

Back side illumination image sensor reduced in size and method for manufacturing the same

I would extend the idea to fit a slotted metal electrostatic screen in between the top metals cap and lower pixel layers to ensure that pixel internal caps are uniform across the array. This would require one more metal layer though.