Spline IK to rigify rig

I have a rigidified character with some extra bones like a tail. I have been trying to find a way to add a spline IK to the bones, but in order to add a spline I must do it in object mode. When I add it in this mode, I cannot access it when I am in Edit mode on the rigify rig. I cannot create the spline in edit mode. I have searched for tutorials, but I have not found anyone who adds a spline IK to the rigify rig. How is this done?

Also, I want to add a spring to this tail, but there is no spring constraint. I saw this in another video, is there an add-on for the spring constraint? If so, where do I find it? Thanks in advance.