The problem is that I don't really have much idea's for any alternative, though currently I'm thinking of animating the pole vector manually somehow using an extra attribute on the foot controller, since I'll be animating mostly by hand anyway.
I was also thinking of somehow making a fully 'manual' knee control, working with stretchy IK, which would let me reposition the knee without affecting the position of the foot... so I could for example still bend the knee a little even though the leg is actually stretching passed its limit. While I have a pretty good idea how this could be done, it still won't fix the pole vector issue.
However I'm very interested in trying out other methods, but my rigging creativity is letting me down at the moment. I'm very interested in any tutorials that cover different approaches to rig the IK pole vector, or perhaps any rig with an unsual knee or elbow setup you might have made... or perhaps the pole vector constraint is the best option.