How to create marks to be used as fake ticks in a fake axis

Hi all,

I used a dummy variable in a scatter plot that served as "fake" x-axis. Why I needed that and how it has been done is described here:
http://www.excelforum.com/excel-prog...plot-area.html
Thanks to MrShorty for that.

Here it is the data set with the chart:
https://dl.dropbox.com/u/20806248/si...ke%20ticks.xls

As you can see, the scatter has two y-series that do not vertically overlap because one of them has a slightly increased x-series (1999.1, 1999.1, ecc. instead of 1998, 1999, ecc.) Now I need to add "fake" ticks to the "fake" x-axis and I believe that a way to do that is just by using a specific kind of marker that is not among those available by default.
I want outward ticks (as appear in the linked graph in the y-axis). I made just a trial by using the crosses marks (that exist by default) and it did not worked as I hoped because the cross was slightly down the fake x-axis (so, another issue to solve).

Hope to find someone able to solve this.
(I use Excel 2007)