Hello Nk,
A good alternative to load images in production would be the manufacturing tool or the newer Universal Update Utility (more information on the link below).
https://community.nxp.com/docs/DOC-344579
These tools take advantage of the Serial Downloader to boot the board and send commands trough the USB port as to load the required images. However, they still require booting the board.
If you wish to load the eMMC without it being soldered to the complete board, you would need additional tooling to send the required initialization and then write to them. I haven’t seen a similar implementation yet.
My apologies for the inconvenience.
Regards,