Mask drag while loading

hi ppl
im trying to make map viewer script.
i have maps in pieces and want to load them one by one on the area where user is browsing
(something like maps.google.com)

what i do is create one mc for each map piece and put all of them in another movie clip and i add a mask on this clip.

i got for each map piece movie clip a loader and what i would like to do is drag the movie clip even if its not finished loading the map image :confused:

the problem is that the mask doesnt apply on the movie clip before it loads its map image…

any ideas,thoughts ?