yay, i managed to boot with:

ITEM_NAME="Mer - Nemo Mobile"
ITEM_ID="nemo"
ITEM_CMDLINE="root=/dev/mmcblk0p1 rootwait rw console=ttyO2,115200n8 console=tty0 omapfb.vram=0:2M,1:2M,2:2M mtdoops.mtddev=2"
ITEM_DEVICE="${EXT_CARD}p3"
ITEM_KERNEL="uImage"
ITEM_FSTYPE="fat"
ITEM_USEATAG="1"

I got some mmcblk0 errors during boot but it managed to get into nemo. But then after a while it crashed by spraying the console with something like:

mmcblk0: error -110 sending read/write comand
mmcblk0: error -110 sending status comand

But that might just be due to my sd card being damaged or something?

Anyway, thanks for all the help!