I like to keep the same resolution all the time on my monitors. It seems that things seem to get a little messed up the sizes and stuff like that so I would rather not mess with it. Getting a monitor extension arm would of course be the most expensive way to fix your problem but it might be something worthwhile. I have been considering one for some time hoping that they would come down in price. If I find one that is $150 I am going to pick 2 up.
http://www.marathoncomputer.com/pixarm.html