I don’t understand why you want to use some actions to control your IK/FK switching.
Anyway, you can add a driver to almost all the values in blender so you can add a driver on the value in the action editor you want to control then a driver can be used with custom properties or “transform chanel”, means translation, rotation or scale of an object or of a bone along one of the three axis.
Little example : with a first object’s translation along the X axis we’re going to control a second object’s rotation along the Z axis.
In an empty scene create two objects : a monkey and a cube
Select the monkey, add a driver on the rotation along the Z axis : in the 3D view on the transform panel right clic on the Z axis rotation value and select “Add Single Driver”
Now you need a graph editor, in the header change the mode from FCurve editor to Drivers.
On the list you can see your driver, it’s called “Z Euler Rotation (Monkey)”
Press N to show the option panel, on the Drivers panel change the type value from “scripted expression” to “averaged value”, lower in this panel “transform chanel” is the default value (you could pick “Single Property” if you wanted to use a custom property)
A field is named “Od/bone:” ; clic on this field and select the cube.
X location is activated, If you clic on it you can change it to more transform chanels.
Now if you move the cube along the X axis, the monkey will turn around the Z axis.
Some things can still be tweaked in the modifiers panel in the graph editor :
- if you change the 1.000 value to -1.000, the monkey will turn the other way
- if you change this value to a value bigger or smaller than 1 the monkey will turn faster or slower.
- if you change the 0.000 value, the monkey will start his rotation with an offset.
“et voilà” I hope this could help to understanding how to control something with a transform chanel through drivers