[GonzaloGil]

You can't, but in fact, there is no reason to. The whole point of advanced options is to store INVENTORY information. Why would you copy your inventory to all your products. I guess there could be a case where you happen to have the same stock of every single item with every single option, but, most of the time, the stock varies depending on the option, so that's why there isn't an option to do this...