Variables - list All but don't pre-select it

I’d like to be able to list “All” in template generated variables, but not to have it pre-selected. In fact, I don’t want to have any variable pre-selected, but list all the individual variables and the All. Is there a way to do it? I tried to blank out the “current” value in the json and import it like that, but it doesn’t work. Any other options?