oh, maybe you could try this :
make a units flying hieght to greater than 0 ( 500 for example)
then using fog at 100(X) and 4000(Y) and a whitish, greyish or light bluish color, than
use the Real clouds doodad ( found on
WC3 campaigns ) and put those in to match the heights of the unit. Maybe itll seem like your walking on clouds?
i dont know ive never tried it... might work..it might not.