IK / FK switch (driven shape keys)

Hi,
can we create a Switch for IK/FK constraint, without needing to manually slide the influencie in the buttons windows, create something in the 3d view like (Driven Shape keys), is there a way ?

Obs: Found this thread, where Kitsu shows how to do it, starting with a separate Object
http://blenderartists.org/forum/showthread.php?t=78736&highlight=driven+constraint+key

Using the technique mentioned above, I tried to create a temporary solution for IK/FK switching
in the new Full Character Rig by Daniel Martinez Lara, posted today:

Here you’ve got the Edited version:

Just an idea, nothing special though.