Rigify doesn't seem to allow me to shift the pole target I've used rigify on a basic human armature, to try and set up IK, and for the most part everything works- except for the elbows. The knees work just fine, but I'm unsure which bone rigify is considering as the pole target. 
I assumed it was the bone behind the elbow- to which the only thing I've done, is move from the front of the model, to the back- and rotate by 180degrees. Nothing else. Is this not the bone? Is there some additional procedure I should be following instead? Thanks.
By defualt the widget that looks like two arrows is used to rotate the elbow/knee. You can also select that widget then click Toggle Pole as indicated in the image. That will enable you to use the standard pole target.