Flashing U-Boot and eMMC over GPIO pins

Good Day Everyone!
Is it technically possible to flash U-Boot and eMMC or at least eMMC via GPIO pins? We are heading towards production and I need to find out if it is possible to provide flashing capabilities without physical interaction.
At the moment you need to press the USB button on the back to flash the bootloader or access the eMMC.
Ideally I would like to have an USB adapter for the GPIO pins where I can flash both (bootloader and eMMC).
Does Radxa itself provide a service where we send our bootloader.bin and rootfs.ext4 which will be flashed before shipped to us? (We are talking about mass production)

Thanks in advance!

Which board are you referring to? Currently on ROCK Pi E can be flashed via GPIO since the USB OTG signal is available from the GPIO header.

I’m referring to Radxa Zero v1.5 1GB/8GB eMMC.

Is it possible to bring the Radxa Zero into USB mode without pressing the button on the back?