1DX Mark II - quickly change modes

I am going to be doing high school football starting tomorrow, and would like a quick way to switch modes.

I will be shooting the game on full manual at around 1/1000 ss, f/2.8, and whatever ISO is required. However, If I see a candid moment (like a coach talking to a player, or a players reaction on the sideline) I would like to be able to slow my shutter speed down to around 1/400 to so I can lower my ISO. So, I can program one of my custom modes to single shot, 1/400, and auto iso, but is there a way to quickly switch to this and then back to manual? The way it is now, it requires me to press the mode button, and then spin the SS dial until I get to C1.
Here is an instance where I think it would be quicker with the mode dial.

Any suggestions?

I am sure you can do that. The 1D4 could. look at programming the * button.
Work in one setup. Use * to toggle back and forth to pre programmed settings.

That's one way. Another is to set the M-Fn button to toggle between modes. It will run through the defined custom modes, and a normal one, depending on what you have enabled.
You can for example program one setting as custom mode 1, the other as mode 2, then disable the rest. Now M-Fn can toggle between the two modes remaining with a single keypress, right beside the trigger button.

The suggestion you got above will probably be sufficient in this case, but it's limited to the things you can program in the custom settings for the buttons. The method I describe will switch everything you can store in a custom mode, and that's quite a lot.