Arduino DUE acting as SPI slave to Raspberry Pi?

Hello,

I need to make an Arduino DUE emulate an SPI peripheral of a Raspberry Pi, to reverse engineer the peripheral. Searched high and low for "arduino due spi slave" but got a lot of peter-pulling without useful answers.

Surely this has been added by now? The motivation for using the DUE is the compatibility of voltage between it and the RPi. At the lowest level, I just want to capture the initialization string the RPi transmits. Less than a hundred bytes at most.

Thanks in advance.