No time for images right now. Really in a crunch. So I'll do my best to explain with plain ol' text.
Start with copying the subject a few times. Gonna need several copies to work with and one left as a back up. Add a background with the appropriate colour.
Add a Layer Mask to one and paint away. Almost all of the background, along the face, shoulder, and some of the hair. Don't paint out the whispies -- these will be done seperately.
Make a selection of some of the whispies. Prolly best to break the whispies into two chunks, but we'll deal with only one for now. Okay, so make a selection of the whispies with green in the background where the leaves (needles?) are. Use Quck Mask or any of the Marque tools. Save this selection in an Alpha channel.
Still on the subject with the selection, hit ctrl + j to copy the selection to a new layer. Add a Curves Adjustment Layer, make no adjustments, click "Okay", and clip it to the chunk you just copied to a new layer. Go back to the Curves Ad-Layer and manually pump up the contrast in each channel seperately.
That means, go to the Red channel, run your Eyedropper thingie over the subject to get the range, then move the upper range up some and the downer ranger down some. You don't have to move the points a lot, but enough to make the ranger wider. Repeat this in the G and B channels. Once you've done that, go back to RBG in the Curves Ad-Layer and widen the range one last time.
By the time you are done with that, you should have some very nice contrast between the hair and the background with a bit of fuzziness.
Remember that selection you made? Load it, and ctrl + shftt + c (copy merged), start a new Alpha channel, and ctrl + v (paste). Invert the selection in the new Alpha channel with ctrl + i (Image > Adjust > Invert). You should now have a solid base to Layer Mask the whispies.
Copy (ctrl + v) the new layer mask in the Alpha channel. Go to the Layer Mask on the subject. Now, in order to paste into the Layer Mask, hold alt and click the Layer Mask. This will show the raw Layer Mask. Then paste it in (ctrl + v).
Repeat the whole process for the whispies with the lighter yellow-green background.
I also added another Curves Ad-Layer to brighten the subject (clipped to the subject so as not to affect the background).
All-in-all, it's a pretty good technique. I've been meaning to add this to Tech-Slop (Whispies 2), but I have't gotten around to it yet. If you give me permission to use this picture, I might be able to knock out a better tutorial by the end of the day. Please...!
Gotta go, but I'll keep checking back to answer questions and to see if you will give me permission to use the picture for my tutorial.