<hack>
Set up an EXTI interrupt on SPI MISO, to interrupt on falling edges.
In the ISR, ensure the SPI transfer is complete, then check and act upon the most recently received data, which you now know contains at least one zero.
Won't work if SPI MISO doesn't stay high all the time, ie. if it goes low when CS is not asserted (use a pull-up), or if it's driven low during the interval between CS going low and the first active clock edge on SCK.
</hack>