Jerry's method is a lot less stressful than mine, as I am willing to put my plants through large amounts of torture to make them look like they were never in a pot. When I mount my plants, the root ball is no longer a ball, the roots are contoured to the mount. I just think they look better not siting atop a 'mound' of brown sphagnum and old roots. I suggest you take your time, to get the look you want. For me, this is the lind of thing I go for:
The root of the issue on Flickr - Photo Sharing!