Here: http://www.fileshack.us/get_file.php?id ... aspect.cap
This example tests the user's desktop resolution to determine if they have a 4:3 (1.33) or 16:9 (1.78) monitor.
The black bars are manually placed based on some simple math.
This example will only go fullscreen if you have your desktop resolution set to a 1.33 or 1.78 aspect ratio, but you could test for other ratios as well and set them accordingly.
I didn't get a chance to test this on my 16:9 monitor, but I'm pretty sure it works (I faked it by setting my 4:3 monitor to a 16:9 resolution and didn't see any black bars when I went fullscreen, so yeah, I think it works.) Even if it doesn't work, it should give you an idea of how to make it work.