Access config flash on Stratix 10 DX development kit

The Stratix 10 DX development kit has a QSPI configuration flash. Unfortunately, this flash chip is not connected to the Stratix 10 FPGA, it sits behind a MAX 10 FPGA that presumably runs the PFL IP. (this is in contrast to other development boards such as the Stratix 10 MX dev kit, which directly connects the QSPI flash to the Stratix 10 MX FPGA)

I want to be able to write to the config flash from the Stratix 10 FPGA (so I can update the firmeware in-band over PCIe). How do I do this? Or is it impossible without modifying the configuration running on the MAX 10?