Very interesting problem as there's only one tag available by object.
In your case (if I got it right), a solution would be to create a Global variable for the Volume.
Then use that variable to set the volume of each sound concerned by that option. (instead of "0" you put the variable)
The tag is free for anything else.
The problem is that you need to replay a sound to apply the new volume. (which is not really a issue if it's done on an "options layout" for example)
I don't see any other solution for now.