Right click the report, go into properties, and there you will be able to check on 'Specify Diagrams at Run Time'. It is one of the options under ER Diagram | Filter By.
The next time you run the report you will get the window that will allow you to specify just the diagrams you want to report upon.
There is also a scale value you can use to set the zoom level for that specific diagram's picture (figure 2).
Figure 1.
Figure 2.
There is also a scale value you can use to set the zoom level for that specific diagram's picture.
