I've made a very dirty edit which unlocks the gallery (still requires the entire mod, I think?), use at your own risk since I've never modded before (took me a while to figure out why it was bitching about tabs lol).
Just replace the original '0brandycheat.rpy' file, load or start a game go into the cheat menu and unlock the gallery (might have to toggle it off then on again).
If it requires the entire mod, then would you also need to replace the script.rpy file? From my understanding, wouldn't messing with that file at the very least, stop further progression of the game than it was modified for?