I decided to give ghouls idea a shot and replace the display with a nice picture from the original Super Mario Land game. Will buy a OHP printable film tomorrow. This way I can print out the picture with my printer and simply attach it in front of the screen. The characteristic screen colour will shine through and the picture will look quit realistic. Not sure about the picture though. I downloaded a speed run from YouTube and searched for nice shots. Then I pasted three into a picture of the gameboy and made them overlay to get the result the OHP film will produce. Here are the three possibilities. Please feel free to choose one, but explain why if it's possible and not just a feeling (post feelings to). I really can't decide which I will choose and need to hear some other statements.
Shot 1:
Shot 2:
Shot 3:
The actual image looks way better, but the resizing tool couldn't really shrink these files down.