Unfortunately, you cannot copy an existing widget within your report, but there is a way around it.
NOTE: This is possible only when creating a widget, not when editing it later on.
STEP 1: Create a desired widget and click on SUBMIT
STEP 2: Now that your widget has been created, you can create another one just like that by clicking on PREV and going back a step to select another source.
This way you can create exactly the same widget with another account.