Just like DotA, when -sh mode is activated, other players cannot pick their Heroes, right ?
Only the host can pick it - in this case, Player 1 (Red).
But since you want it Player 2 (Blue) to take the lead, only Player 2 can pick the mode, right ?
In this test map, you will 'act' like you're Player 2 (but you're Player 1 - because AI cannot be forced to type a message chat).
Here's a test map.