I did some prototyping of this using overlays. It is possible using
overlays, you can find the horizontal axis points and move a div to that
area.
chart_ctl02.getChartLayoutInterface().getBoundingBox('vAxis#0#gridline#0');
But this doesn't pass my usability test. I wouldn't want to have to do
You can do something similar with domain-axis annotations, which allow you
to create labelled vertical lines on your chart. They are not customizable
to the extent that you are looking for, though (you can color them, but
they will all have the same color; you cannot change the line width).
