Using a second monitor as a projector (aspect ratio issue)

I have a laptop with Windows 7 and a 1920*1080 resolution. I am trying to connect my external monitor, with a 1280*1024 resolution as a projector - but want to maintain the aspect ratio of the laptop (I need the full widescreen to do my work, while someone else watches on the second monitor).

I would like for the second monitor to show exactly what is happening on my laptop, but with black bars at the bottom and top to account for the difference in screen size. I cannot seem to find how to do this - my laptop automatically adjusts to fit the external screen's aspect ratio (vertical black bars on the left and right of the laptop), and when I manually change it to the 1920*1080 resolution, the external screen stretches instead of developing black bars at the top and bottom.

I would really appreciate any help! Thank you