Apo 7x15 and Chaotica
The technique i used to add bubbles is described here (check 3rd example):
Shared linked transforms - ExamplesHere we go, a collection of examples of shared linked transforms usage.
Those are not all, just some exercises and examples of what can be done using weights.
Elliptic Splits
Lets start with a basic Elliptic Splits pattern:
Tutorial - Splits ellipticBasic Elliptic Splits - starting parameters

Now, lets add a shared pre linked sphrical transform.
Add a new transform (xform 3)
Set its opacity to 0Set its color speed to 1 (optional, you need this so it does not affect the coloring)On xaos tab, set the weight of xform 3 to itself to 0On xaos tab, leave the weight from xform 1 to xform 3 as 1, and set everything else (to itself and to xform 2) to 0Repeat step 6 for xform 2At this point, your fractal should look the same as it was before you added xform 3. If yes, replace linear with spherical. Else, check previous s

In a few words, you add a pre-linked transform with pre spherical + spherical + eyefish, and then fill the resulting hole

http://tatasz.deviantart.com/art/Trees-575036203