I want to display dashed vertical lines in a graph control that run from
the x axis to the top of the y axis at specific points along the x axis.
I've tried several techniques, none of which have worked.

-Drop lines seem to be either off or on for everybody. If I could get
them to work for only one series, I could put some points along the top
and it would work.
-I tried using a series with a dashed line to connect two points, one at
the x axis, one at the top, but I can't have two points with the same x
axis value, and no matter how close I make the x axis values of my two
points, I get a little jaggy in the line since it isn't truly vertical.
-I tried making several series where each series would have exactly one
point in it, which represented part of the line, with the intent on
making the symbol for each of the series be a vertical line (so each
point would be one dash in the dashed line.) Alas, there isn't a symbol
suitable for this purpose.

Anyone else have ideas?