Not an en dash, but you could add a Rule Above as part of the style and set a really large right indent.
Thanks Peter. I had a go but it seems there's no option to fix the rule length. It will always vary according to the column or text width.
That's correct, but if the column width is known you can set the right indent to whatever is appropriate for that column width. You'd have to edit the style if you change column widths. If there is no consistency, then you can't use this method and you'd need to do something like Find/Change to add the dash and a return before the paragraph.