Hi.
I don't have any Wii U without a gamepad, but I use a controller to save gamepad battery.
Anyway, I tried to go into the Environment Loader Menu using the pro controller (by holding X on the pro controller) and I was unable.
I think this is a potential problem for people unable to get a gamepad connected to their console.
This could be solved if there was an icon in the Wii U menu leading into the environment loader menu, or if holding X on a pro controller (or another controller) while loading would lead to the environment loader menu.