A custom model is also an option for skipping the necessary channels.
I posted this over on falconchristmas, before I realized you were asking here as well.
http://falconchristmas.com/forum/index.php/topic,4475.msg47237.html#msg47237
Yah but for my sanity and ocd I don't wanna pack the pixels. I like to keep it nice and easy for me to remember and see. Like if the right side of arch one goes out. I know it's universe three.
Everyone has idea's about what makes sense to them, but my personal feeling is having contiguous channels for models in xLights helps avoid issues outside. You can get both worlds if you want to just specify 360 channels per universe as Dan indicated above.