Programming a JN5168-001-Mxx with a USBtinyISP?
Maybe I am late to answer this, but thought to share the ideas for others who may come across this question.

You can use FTDI FT232RL or any such USB to TTL converter, connect Rx/Tx of one with Tx/Rx of other, pull down pin 3 (SPIMISO), then pull down Reset (Pin 22), then release reset and then release SPIMISO. This sequence would put JN516x in programming mode. Starting the flash process then should transfer the code to your device.
You can write a program to control the serial port of your computer, using which you can control various additional pins of FTDI to create the above mentioned sequence to put JN5168 in programming mode. For example, you can make use of CTS, RTS, DTR or other pins

Hope it helps