Thanx for the help.
Pardon my ignorance but I need to ask this:
What do you mean by "animating the mask"? If it is giving simply keyframes to the dots in the mask and for the larger or smaller version, changing their positions, I tried it before. It works, but not satisfyingly enough especially considering the effort it takes. :)
In another forum, I found a similar issue:
http://www.videocopilot.net/forum/viewtopic.php?f=4&t=48202
The solution suggested there is a bit complex for me but I will have to follow those instructions in case there is no easier meat. :)