Here's another answer that doesn't do what you want either, but may be useful.
C-x v g
runs the command vc-annotate
.
That'll pop up a new buffer (I know, you didn't want one), but it'll have all the lines marked with who touched them when. And, bonus, they're color coded with a heatmap (red is most recent, blue is least), for easy identification of recent changes.
Of course the built-in version of vc-annotate doesn't scroll the buffer appropriately, so you'll want this advice:
(defadvice vc-annotate (around vc-annotate-and-scroll)
"scroll buffer to view current line in the annotated buffer"
(let ((pos (count-lines (point-min) (point))))
ad-do-it
(let ((orig-window (selected-window))
(window (other-window-for-scrolling)))
(select-window window)
(goto-line pos)
(select-window orig-window))))
(ad-activate 'vc-annotate)