Disable interaction with an UserSerie

[Zandor300]

I am rendering a chart with 2 series;

• Actual data I want to show. Data can dip below 0.
• A series that draws a line along 0.

This line at 0 is there to exagerate that the data drops below 0.

What I want is to disable interaction with the line that is drawn at 0 so that when the user's cursor is closer to the 0 series than the data series, it will still focus the data series.