1. after you have finished your large plot, select the layer by clicking once in one of its axis. It will show "selected" with a bounding line and small black squares arround.
2. Copy (Ctrl+C) and paste it (Ctrl+V) again, so you have two equal layers.
3. Select the second layer and resize it, place it where you want inside the first one, and make the changes you need in the plotted Y-X range and so on.