You could use a macro that asks for the first and last cells and fills them automatically. Something like:
Sub FillMe()
Dim LastRow As String
FirstCell = Application.InputBox("What is the cell you want to copy?")
LastCell = Application.InputBox("What is the last cell you want filled?")
Range(FirstCell).Select
Range(FirstCell).Copy
Range(FirstCell).AutoFill Destination:=Range(FirstCell & ":" & LastCell), Type:=xlFillDefault
End Sub
If you use it enough, just add a button for it to your toolbar for easy access.