Is there a way to set the slot of a key mapping

I’m setting up key mappings in my game and I’d like to have primary and secondary keys. I know that there’s a slot you can assign the key mapping to at runtime, and it seems that all key mappings setup in the editor are set to slot 1. I’d like to know if there’s a way I can set a keymapping to slot 2 in the editor. For example you have ‘W’ would be the key for forward movement in slot 1 and ‘Up Arrow’ would be slot 2 by default.