setMask using mouse trailer (MX)?

i have had this file sitting around a while and what i would like to do is make the blob/bubbles mouse trailer actually set as a mask for an image or mc.
all the code sits on a small control clip just outside the stage.

here be the fla - blob.fla

also any hints on how to get this little thing to work in MX 2004 ?
thanks in advance
sky