Assuming you have the same SoC as in the pictures in this thread, try something with AR7161, there are a couple of those available.
Set up a TFTP server based on the printenv settings in uboot, then try the bootp/tftpboot of an initramfs image.
Don't forget to document everything.
Looks lika a good start, but you'll need to compile your own initramfs. If you do, include support for the LAN chip in the process.