Whilst you can restrict the screen size quite easily, you will find that the laptop tries to be "clever" and adapt to the restricted size.
A partial way around is to go into the laptops BIOS and set it to not try to make lower than native screen resolutions fill the screen. Not sure what the actual phrase will be in your particular BIOS.
When you have done that, the laptop will try to centre the image on screen rather than automatically scale the image up to full-screen. This is still an issue as you will need to loose twice the amount of broken screen. But at least you will be able to see everything.