How to create a full *.bin dump with OpenWRT to directly flash it on ROM chip without serial console or firmware bootloader

I want to upgrade some old TP-Link WR842N V4 from 1MB to 16MB ROM using a W25Q128 same like it is described for the TP-Link WR 841 in this nice video from Freifunk:

https://www.youtube.com/watch?v=l6rw1zo4A2c

The board even already has 64MB RAM (A3S64D40GTP-Zentel chip) and a QCA9533 processor. So from all the information I found on the internet it should be able to run an OpenWRT on it with the 16MB boot ROM chip. Unfortunately, I can't access the serial console, because some bridges on the board are missing. I have a EPROM programmer at hand, so I am able to read the old ROM, saving the last 64kB for the MAC and the artdump. I found some description to install a modified bootloader, like pepe2k, but all these manuals involve having access to the serial console sooner or later, e.g. to start the httpd in uboot mod, so that the router can be accessed from the network instead of the serial console.

https://wiki.freifunk.net/TP-Link_WR841ND/Flash_und_RAM_erweitern_bis_v12

Is it possible to build a complete 16 MB *.bin "from scratch", including bootloader, OpenWRT and the artdump information and flash it on the chip, then place the chip on the board and start the router into OpenWRT right away? The factory software does not allow to boot anything but original firmware and also the 1MB is too small for OpenWRT. Although it seems there is a uboot like bootloader in the original firmware present, because somewhere in the bin file there's a string "u-boot image".

Maybe the information is already somewhat out there in the OpenWRT Wiki, but I am not able to bring it together in the right way.

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