Harmony bootloader use SPI instead of (USB device, host, UART, etc.) (Zhe Hu)

I have a certain hardware configuration that PC USB <--> MCP2210 (SPI master) <--> digital isolator <--> PIC32MZ SPI slave I am wondering if it's possible (& how) to update firmware via PIC32MZ SPI (as slave). With the current MHC, it's about selectin..