Maxattack,
I hear you on that one. I am 'apple' shaped (working on that-lost almost 40 lbs already) and I have no rear. All my fat is around the waist and on the underarms and there is nothing padding my behind. Took forever to find a saddle. I found the soft ones let me sink in, which sounds nice on paper, but without support it hurt a lot. The RXL I finally tried (see my post in this thread if you haven't already) is very thinly padded and hard and slightly radiused side-to-side. It took some 8 rides to get comfortable. I don't know how much you have ridden your RL, but if it has only been a few rides, keep at it unless it is really unbearable. If you need more cushion, are you using good shorts? I can feel the difference between my cheap Fox shorts and my good Specialized ones. Good shorts are worth every penny.

Also make sure that your seat hight, fore-aft and tilt (should be level) are set correct.