Toggleable Function Layers

[hazy topaz]

I've seen this suggestion around a bit, and honestly I think this would be a useful option. You press the function key once, and the keyboard switches to that function layer, you hit it again and it goes back to the main function layer (or previous function layer). It would be helpful for say, a numpad on the 60HE on a function layer that you don't have to hold a button to access.