It will still be only a Y displacement map, so you can't have the (3D) blobs that constitute clouds as a map. Basically converting the PF into a terrain is indeed the way, if that's what you want. If either black and white are unclamped (in cloud density fractal they are), and you displace accordingly, you can turn off all lights, set an altitude over which a greyscale will fade from black into white and plug your displacement to scalar into luminosity input. Then the blackest areas will be the 'minus blacks' and the whitest areas will be the whites above 1. Just play with the fuzzy zone and altitudes, so the mid area is mid grey (whatever that is). If you save an ortho render as 16 bit (I don't know if it's possible to save as 32bit), you'll have your map with quite a depth range.
But I doubt if this is the best way to handle this, and if it's any use.