A while back I wrote a hack for someone else that might work for your needs:
http://jsfiddle.net/asgallant/KJavc/. As is, it's not quite what you want, but it can be adapted to use line series instead of area series to put vertical lines on the chart.
On Wednesday, January 9, 2013 8:38:02 AM UTC-5, Vor wrote:
Is it possible to separate the groups (on a discrete x-axis) visualized in a Column Chart with a vertical gridline?
(the resulting chart would be MORE readable)
Thank,
Vor