Why don't you use the Notepad++ multiline editing capabilities?
Hold down Alt while selecting text (using your usual click-and-drag approach) to select text across multiple lines. This is sometimes also referred to as column editing.
You could place the cursor at the beginning of the file, Press (and hold) Alt, Shift and then just keep pressing the down-arrow or PageDown to select the lines that you want to prepend with some text :-) Easy. Multiline editing is a very useful feature of Notepad++. It's also possible in Visual Studio, in the same manner, and also in Eclipse by switching to Block Selection Mode by pressing Alt+Shift+A and then use mouse to select text across lines.