Widescreen game in fullscreen

I'm working on something here and was considering putting it into widescreen (16:9 specifically) due to viewing area problems.

However, this seems to pose a problem. Construct just doesn't like it. The game was originally 320x240. Enlarging the screen size horizontally until we get to 16:9 makes it 428x240 pixels, which is actually a pretty nice viewing area for the retroness the game has. Of course, full screen absolutely hates it. I know that 428x240 is not a resolution monitors would support, so I understand that it will warn me and change to the next available resolution (512x384 I believe the warning says). The problem with this is that it stuffs the game's area into the top left corner of the screen... can it be centered or something? I'm trying this on a 5:4 monitor by the way (1280x1024 max resolution) so I have no idea what it would do on a widescreen. The idea is that it would be centered on 4:3/5:4/etc. monitors but on a wide screen it would fill most of the screen (obviously not all of it due to the kinda weird window size I set, but it would at least conform to widescreen)

I'd really like to improve the game's playability with widescreen, but I don't want to shutter off full screen because many people like to play games full screen...

You could fake it with black bars.

I had an example a while back that showed how you can change the x and y zoom by different amounts to go from 16:9 windowed to letterboxed 4:3, but ioj ate my fileshack file when they bought the site and I don't have a backup.

Basically the example had a layer on top with black bars at the top and bottom, only you couldn't see them in windowed mode because they were off the edge of the screen. Then if you go to fullscreen, there was a quick check to test the aspect ratio of the player's monitor based on their system's screen resolution. If it was a 4:3 screen, it resized the resolution accordingly, and the black bars would then be in view.

If you have a layer with a HUD you might need to manually scroll it down or something. And you might need to mess around a little with centering the view on the player, unless you have unbounded scrolling.