I was planning a project on MRK ZERO and realised I was running out of ports. As it happens, SD card has dedicated SPI1 interface connected to it. If you are not using SD card you can plug in SD slot extension and solder to SPI1 pins, giving you 4 extra ports. SS pin has hardwired pull-up resistor of 100K, but it is not a problem. Here, tested the idea and it works:
I changed design a little since and have 2 spare pins now without using SD slot, which I still don't need.