Can't you just put a delay (like 30 seconds/1 minute) on the stream? For example using Open Broadcaster Software which is free there's an option called "Delay".
1 Minute is not enough to keep streamsnipers away (since automatch usually takes longer than that to find a game). And a delay doesn't work for the streamers that like to interact alot with the chat (Like Hans and Stephenn for example). That would get 'out of sync' so to say
Only solution would be a 'gentleman agreement' ^^ If you want to streamsnipe, atleast tell them who you are at the start of the game. Atm you only hear them brag when they've won. But if they lose you'll never hear them ofcourse. Which is really lame..