I don't know much about it but I've read/heard that Gateway's Launcher.dat couldn't be loaded in the same ways as people load rxtools.dat or cakes.dat
Without internet, for O3DS the best way would be to downgrade MSET to 4.x or 6.x so you can use MSET exploit (not as good if you play DS games on it), or on N3DS, the OoT3D GW exploit (MSET will -not- work on N3DS, and I believe installing 4.x or 6.x system settings app -may- cause a brick.)