There is a little-known feature in OnePager that allows you to turn several tasks into a single task…this is called the Virtual Summary Task, or “VST.”
To create a VST, simply select as many tasks as you would like to combine using your CTRL key or using a mouse-lasso. Then right click on one of the items and choose “Make into virtual summary task.”
In the example below, notice how you will end up with a single task bar.
This VST is something you can then right-click on to “unmake” it, modify the %Complete value, or double-click on in order to change the task label.
Lastly, once you’re through creating the VST, eliminate your empty rows by clicking the Hide Rows button on the Home tab in the ribbon.