sorry I forgot the static grid part... clouds are really just textures mixed with opasity set to center gradient... which means nothing will effect it. You have to paint your clouds in. This is hard, but you can do it. more or less you need to. If you use the 3d nuke preset and delet everything except the fluid container. you'll have a nice texture for your clouds already. I'd chenge these settings:
damp - .1
turn temp to off.
incandesence set to density (make the red and yellow ones dark grey)
there's probably more but that should get you started.
painting the density in can be a pain, what I do is (before you turn up your damp) pain it in turn up your sim scale rate and let the fluids flow for a bit. then put the settings back.
Once you make this, and it looks ok, start over and it will look better. you can add temp to the equation to make the clouds move more into place.
Again this is a hard effect to get to look good you need a high resolution to get the motion field to look good and move the clouds. Oh geez, is this making sence? I feel like I'm babeling.
Maybe someone can give you an easier way. It's just that the clouds need to be dynamic grid and the opacity to density, or it won't move. then you need to make your own clouds since clouds aren't set up to move like that. Sheesh!