The easiest way would be to use helper column using either numbers 1 to 3 or any formula that indicates this is the row I want to use in my chart. Then add thite pivot table normally and place the helper column into the page field. From there it is easy to filter out all the unwanted rows and only display the rows you're interested in.
I'd also recommend that you format your dataset as a table before creating the pivot table. This way the formulas copy down automatically and you can simply refresh the pivot table every time your data changes.
