Creating a dynamic line in a row

Hi

I'm trying to figure out a way to make a line that covers the entire row and sits in the middle, until a text is typed, then it starts to get shorter until it should eventually disappear as the text fills the whole row.

I've tested lot's of options but none of them provided a desired solution, such as inserting a text box which just get's pushed onto the next row, etc...

Unless there is a setting directly in word that would allow this, it might have to be a job for VBA, which I've never tried before. if anybody knows how to achieve this I'd be most grateful. 

Visual representation of the desired effect in the picture bellow done with line shapes and manual adjustment.