I'm not sure the right clic thing is the best way to do, but Ubuntu and Gnome definitely need a proper font manager. The accumulation of different kinds of font (postscript, bitmap...) in different systems (OpenOffice will have different fonts than Latex...) looks really messy.
What's the problem with a nautilus script which copies the file into the ~/.fonts folder?
I am using KDE too, but THAT can't be a problem, nautilus has script plugin support AFAIK.