The Location information can be obtained easily enough by creating a vertex group of the face you want to constrain to, then enter it into the Copy Location constraint. But the rotation constraint will always produce wonky results.
I did also try it in a recent build of 2.5, and had the same results. So hopefully this is something that the developers plan to sort out maybe after the initial release (if it doesn’t cause a problem for durian, in which case they would probably fix it quickly).
There are other ways to get orientation information depending on your setup though…
On the suzanne rig I made for example, the bones that are constrained to a seperate face mesh (in the same way as what you are wanting to do here) are copying the rotation from the control bones in the first armature (there are 2 armatures in the character - body and face). For example the bones on the lower lip in the second armature all copy the rotation of the lower lip bone in the first armature (*note that the constrained bones are not the control bones).
Another technique I recently used was to create hooks on both sides of a mesh to determine the direction. You can read more about that setup in this post. This setup takes up quite a bit of processing power though, so use it sparingly.
Notice: You cannot deform the object with the same armature that you use to constain bones to the surface. That will cause a dependency loop, since the whole armature and all its bones are evaluated at once.
If you come up with better solutions, please do let me know