I don't know if such feature is available on any casino, haven't seen such anywhere, and I am eager to know what you guys think about such a feature, and feel free to use this thread to suggest other features you did like to see in our online casinos.
Basically, you want an automatic cash-out if your parley reaches x2,x3...x10 at some moment. I have never seen anything like it, and I doubt this will ever be available. The question is how many people would use it, and whether it would be a popular option for punters. If it is not something that can attract a large number of people, I doubt that the casino will bother to create it.
You only have one thing left, and that is to follow your games and cash out manually at the moment you want.