If you cut the end of the molding at 45 degrees (as if you were going to join the corner THAT way, INSTEAD of coping ... and maybe not that severe of an angle is necessary - 20-30 degrees may be sufficient) - you can see the contour of the molding better. Then, lay the piece flat and follow the contour with the coping saw. Put a slight back-cut on it also (5-10 degrees.)
Make sure you factor in the lenght of the piece you need properly - the mitre used for getting the countour may throw off your measurement if you're not thinking about it.
Hope that makes sense. It's pretty easy using this method.