Add "empty" first value to dynamic value list

I could swear I've read how to do this, somewhere, before, but now I can't find it. My problem is this: I have a Value List called PeopleNames which uses values from first field "Person::id" and second field "Person::name". "Include all values" and "Show values only from second field" are both selected.

Now, in my layout, where I use this value list to select a particular person (which I use for filtering a list of things), I want to also include at the very top of my menu of PeopleNames an "empty" value, or one that says "*ALL*" or something like that.

* I don't want to have to create a blank dummy entry in the Person table (with Person::name = "" or Person::name = "*ALL*") in order to do this.

* I know that the field associated with my PeopleNames menu could be blanked-out if I select the menu field then hit the "delete" key (or create a button to do the same), but the user interface would be much more intuitive if the pop-up menu actually contained the "blank" entry.

Is there any way to do this, to add a blank initial value to a menu which is based on a dynamic Value List?