Ian,
The basic problem is that the camera cannot accurately record the full range of tones as your eye sees them under the lighting conditions you describe. Regardless of the camera mode you use, this will be the case. If it's too bright in the sky or too dark in the woods, unless you use a ND filter (to reduce the brightness of the sky) you can have one bit accurately exposed, but not the other. This is a well known problem for wedding photographers where there are black suits and white dresses in the same scene.
You have to tone down the bright bits to get the whole scene to be within the dynamic range capability of your camera. Use an split ND grad filter, placed ONLY over the bright bit of the scene to record detail in the sky.
You could try this:
http://www.worldphotographyforum.com...ead.php?t=3427
but if there's no detail there to be recovered, it won't pull something from nothing.