Hi Adavis,
Have you found a way to draw a threashold line/target line yet?
Here's what you can do...
In the table, right click on the Y-axis.
Select "Data (Y) axis options".
Go to [Gridline] tab, you shall see the last check box "Draw custom line at". You can set the value to 90, then you will see the target line at 90.
If you would like to change the target line - different colour, etc. Right click on the target line and select "Format user line". I find it easier to right click on the line if you enlarge the report.
Hope this help!