Thanks for your reply! I meant the first one, a title for the whole widget.
I found a workaround, it’s very ugly/hacky, but adding the title to the custom JS as follows:
$("#wpfwoofilterswidget-17").before( "<div class=\"widget\" style=\"margin-bottom:0px;\"><span class=\"gamma widget-title\">Filter</span></div>" );
gets the title to only show up when the widget is actively displayed.