[Plugin: Taxonomy Drill-Down] When using drop down box, put text in the empty box

I have been experimenting with the drop-down version of the widget.
The drop down defaults to a blank selection. I would like to put some text in there like “any” or “all” to indicate that if you skip it and select criteria below it, you will include everything at that level, or not exclude anything (at least that’s how I think it works).

Any suggestions?

Thank you!