How to fool X to use only part of the screen?

Hi,
Earlier today, all of a sudden the screen of my laptop got broken. Luckily not completely. There is a vertical white band over the screen at the right side. I can still use the laptop by using only the left 70 % or so of the screen.
It is of course annoying to resize windows the whole time to the correctly working area. And for some interface elements that is not even possible. So I was hoping to be able to make X only use the left 70% or so of the screen only. That reduces my screen real estate and would give me a strange ratio but would save me a lot of trouble. But I did not find any way how to do that.
Anyone who has an idea. I'm using KDE and I'm not scared to dive into config files.
KR,
Sitor
Earlier today, all of a sudden the screen of my laptop got broken. Luckily not completely. There is a vertical white band over the screen at the right side. I can still use the laptop by using only the left 70 % or so of the screen.
It is of course annoying to resize windows the whole time to the correctly working area. And for some interface elements that is not even possible. So I was hoping to be able to make X only use the left 70% or so of the screen only. That reduces my screen real estate and would give me a strange ratio but would save me a lot of trouble. But I did not find any way how to do that.
Anyone who has an idea. I'm using KDE and I'm not scared to dive into config files.
KR,
Sitor