I've been wondering about this sort of thing for a while now. Before I couldn't figure out how to do it with my bridge camera, a Fuji Finepix S7000.
So when I got my K30, I was hoping it would finally be possible to have 2 separate functions. After reading this I became disappointed.
However, playing around with the button customization, it seems I was able to get them to work separately --- unless I'm missing something (which I probably am ;-). I set the 'AF/AE-L' button customization to 'AE lock'...
Now when I press the shutter halfway, it will lock the focus, but not the AE - I press the AE-L and it will lock the AE.. If I then let go of the shutter (while keeping AE-L pressed), I can press the shutter halfway again for another AF lock - while the AE settings still remain locked from when I first pressed AE-L.
Could this newbie have cracked the problem???
(Somehow I doubt it... I must be missing something, but don't know what yet. :-/)