We should be able to add vertical flip and horizontal mirror output to the sensor class. OmniVision sensors support this. The OV7725 does I know. For the OV2640 you can find the data sheet by googling for it here: http://www.uctronics.com/download/cam_module/OV2640DS.pdf
See Page 22. There’s a vertical flip and horizontal mirror register. So, use the register read and register write stuff for now. Its reg 04, bits 6 and 7.