How to clone display to external monitor with custom resolution during boot?

NOTE: this question is not about configuring desktop manager (like KDE3), it is about booting up the system.

The hardware configuration is this -- laptop with high resolution display, and external monitor with low resolution display. I run openSuse 13.2.

The problem is my main display is broken, so the effect is this:

• GRUB stage -- I cannot see anything


• booting -- the display is cloned or extended, I cannot tell the difference


• desktop manager -- thanks to GUI setup I was able to configure both monitors correctly

My main concern now is booting phase (second step), openSuse uses GUI mode at this point so I hope it is possible to configure the system to use different resolutions per each monitor, and clone the display.

How to do this?