You can let the infected bubbles to the right spread down, as you will be able to use an angle shot later to take it down. Be careful to not let the infection spread downward past the original lower margin, however, or you won’t be able to see the star level at the top. I would recommend at least the Magic Potion 7 extra Bubbles
The picture has not the angle shots in it, but it is pretty obvious, I think. The whole midst level is actually just angle shots via the left wall!
[ update March 7, 2012 ] Alternate Tip for making 3 Stars:
I used the 3 holes in the ceiling and the Rainbow Bubble too. I started by clearing out the lower level’s “teeth”, then I played as explained earlier.