line graph tooltip with vertical line cursor

[conrad]

If you have a vertical line cursor on a stacked line graph, and have a
tooltip showing the data positions, the tooltip will contain the X
value for every series. This is duplicate data, because the cursor is
selecting all series on the vertical line. So you might have a tooltip
that reads:

Series1: May 18, 100
Series2: May 18, 45
Series3: May 18, 99
Series4: May 18, 22

Is there a way to remove the X value from each data point in the
tooltip, and instead display it at the top? Ideally, it should look
like this:

May 18
------------------
Series1: 100
Series2: 45
Series3: 99
Series4: 22


I can format the string on the tooltip, to look like this:

tooltipFormatString : '%s <span style="display:none">%s </span>%s',

Which will only display SeriesN: y (although maybe that's a silly way
of doing it?), but I can't find anything in the docs about displaying
the X value only once.

Thanks!

[andrew]

I know it's been about a year since you posted this question Conrad, but any chance that you found a solution.  I am stuck with the exact same problem.