Paste the bright and dark stock images into the composite as separate layers. After desaturating the stock images, perform an edge detect (Filters -> Edge-detect -> Edge... -> Sobel), then a Gaussian blur to remove the rippliness of the edge-detect (Filters -> Blur -> Gaussian Blur). Use this image as your layer mask as before.
Perfect tutorial although did not understand the the other way that you described (tone mapping). I tested the procedure on some photos and works perfect.
This is very well done. I will be attempting an HDR process in the next few days using these instructions. If I have problems following the instructions, I'll let you know. Thanks very much!
Thanks