* Be careful to follow the instructions exactly. I take no responsibility for bricked Wii U's.*
This mod will allow you to install the custom firmware on NAND so SD will not be required.
Follow the usual method to install the Haxchi rom.zip.
While still in WUPclient, create a directory to store the firmware in.
w.mkdir("/vol/storage_mlc01/FW",644)
then copy the firmware from SD to NAND
w.cp("/vol/storage_sdcard/fw.img", "/vol/storage_mlc01/FW/fw.img")
if it does not copy from SD you may have to mount the SD.
mount_sd()