Advanced CSS challenge: underline only the final line of text with CSS

Question

I want to underline the final line of multi-line text, or at least create the allusion of it. Look closely at the following examples, because I\'m trying to do something tri

Answer 1

Disclaimer: Chances are that this is not possible, but please consider this answer to be thinking out loud / suggestion of a place to start looking, than than working code.

Is there possibility of highlighting the lines of text (with a colour that matches the background colour) and then adjusting the line-height such that the background of the lower lines overlap the underline?

Pictures say a thousand words, so take a look at these:

Before:

After:

From these mock-ups you can see that there are a couple of caveats and do not match exactly what is being asked for, but perhaps this is a starting point..?