Don't know what 2D editor you own, though my personal preference would be 2D postwork in PSCS3. Trying to do this in Bryce I would imagine to be pretty tough.

First off, unless you plan on adding a level of detailed creases, wrinkles, & folds throughout the scene, highly accented detail in one area is going to appear out of place. My advice keep it minimal. Some highlights and slight shadow together to represent light effecting the detail in cloth should work well.

Create a second layer of the image or better yet a masked figure created using the mask option in Bryce. The layer that will be on top will get desaturated, as grayscale works best to change light properties and not alter the original colors in the subject.

You'll be using the Dodge and Burn tools with a soft edged brush, the settings I used are shown, but experiment till you find your preference.

The Top layer Effect setting will be on "Luminosity", this will only effect the lighting value of the image. But if you use the entire image instead of just the subject, you'll create lighter spots throuout the image.

Nothing fancy, took me five minutes to do this for a quick demo.

Finally, I would suggest take a look at some Fashion Photo shoots to study how light falls on Cloth across different areas of the body, suprisngly it tends to emulate the anatomy's own flow lines. Where in this image you have Ribs, Abs & Pecs.

Good luck and keep us updated.
ICM

ps
Shout if you have more ?'s

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Ockham's razor- It's that simple