it is possible, but it will not give you the result you are thinking of.
the user has one replaceable faderbox (thats a false-colored cubemap) which can be used for that.
still the colors can be ajusted by the skysystem, but in general its better to use it as its ment to be used.

i am planing to create another version which uses common skycubes (as well as faderboxes) and single (model- and/or sprite-based) clouds.