iTunes videos on a different harddrive?
In your Music directory, go to iTunes/iTunes Media/Movies - copy the Movies folder to an external drive.  Then replace the Movies directory in iTunes/iTunes Media/ with an alias that points to the Movies directory on the external drive.

What you'll end up with is iTunes thinking the same directory structure exists, but the Movies alias will point to the external drive.  You may not even need to re-add anything to your library - the file paths should remain the same.

I have had my iTunes library set up like this for years for the same reasons you list.

Instructions on creating an alias can be found here: http://support.apple.com/kb/TA26514?viewlocale=en_US