How do I enable/disable graphics card at will without logging out?

view story

http://askubuntu.com – My battery backup hardly lasts for 45mins. I searched for a similar problem but din't find any solution applicable to me. I use Nvidia GeForce 525M graphics card and use nouveau. My laptop gets heated up to about 85 deg (according to jupiter). Such a power consumption is too much for my battery. Is there any way I can enable my graphics card and load my kernel module only when needed? And till that time use only the integrated Intel graphics card. (And I do not mean blacklisting as I would have to log out to enable it) (HowTos)