How to manually assign gamepad or keyboard input to player controllers?

In a singleplayer game where there’s only one player controller I just need to set up the controllers in the ‘Input’ section under Project Settings and it will work.
But what if I’m making a local multiplayer game? Afaik, the only control I have over which player controller get what is by checking or un-checking the ‘Skip assigning Gamepad to Player 1’. How can I let the each player choose the type of input device they want. For example in a 3 player game, have player 3 choose the input to keyboard and the other two use gamepads? Or even in just a 2 player game, having player 1 deciding for himself if he wants to play with a gamepad or use keyboard, instead of me ‘forcing’ either option on him by checking or unchecking the ‘Skip Assigning Gamepad to player 1’?