Well, basically, use Mt Gox on clearnet - always - and use SR on TOR - always. When you need to send coins to SR, withdraw them from Mt Gox and for the bitcoin deposit address, use your SR deposit address (found on your account page over on SR itself). There is nothing about your SR wallet that identifies it as such -- so you don't need to worry about Mt Gox knowing that you're sending to SR, because it can't. And, once the coins hit your SR wallet, they are automatically mixed by SR's built-in coin tumbler.