Easy: you log out of the present session. Then you are without a visible screen and can login again. ,,Normally" one could do it as well like this:
into a root Konsole you type ,,init 3" which stops the X-server. Then you have to serve the processing of compiling the driver package by konsole means. This I tried today in vain under Mandriva. With Slitaz it is much easier as they already offer a ready driver via tazhw. Just click on ,,nvidia" under ,,Hardware". The rest is automatic.
But => again you have to leave the session for a moment to adjust the Xserver anew.

Well what I was looking for was the ctrl-alt-backspace trick, which I eventually found on the internet but thanks for the post!