Found this old forum post.
#!/bin/sh
ftp -n 192.168.178.1<<EOT
user adam2 adam2
debug
bin
passive
quote MEDIA FLSH
put /"your path"/bin/lantiq/openwrt-lantiq-xrx200-FRITZ3370.eva.align.128k mtd1
put /"your path"/bin/lantiq/openwrt-lantiq-xrx200-FRITZ3370-jffs2-128k.image.eva mtd0
quit
EOT
seems to have kinda worked for MatrixCoder.
I was a little irritated by the notion to install uboot, but the files for the FB3370 distributed by lede suggest that.
The last OpenWRT release for this FB offers the files used above instead.