Underline a form control text box full width?

[AndyNoCo]

Is there a way to have a form control text box underlined for the full width? It would be like if there was a "bottom" option in the text box properties "border" setting. Or, if the text box could be underlined like any other character.

Right now, if I set the text box position and size to "as character" and set the properties font effects to "underlining: single" only the characters are underlined. If the centered text is shorter than the width of the text box, there's a white space on either side. I need that white space to be underlined.

[Villeroy]

A line from the drawing toolbar may help.