I don’t know about the DX80, but if you keep the handle on the X80-GT it’s comically easy. The button is opposite the handle.
I grab it like this: Holding X80-GT - Album on Imgur and then once I get it to the setting I want, I hold it by the handle.
If your hands are too small to hold it that way, keep the handle on it and scoop it up with your thumb like this: Holding the X80-GT part 2 - Album on Imgur and your finger naturally rests on the button.