let me know how you ended up doing this, of course its been 2 years since this was posted and Adobe CS6 is out now, my new project was doing exactly what you want but spherizing the heads to look like bubbles, problem is CS6 has a bug, whenever i Spherize anything it defaults its position to the center of the screen instead of respecting the timeline automation points i made to fallow the head around or track it.
now this video i am referring to is with music, someone singing, a scene so here i will lay out a basic asset pre post work flow., like alice in wonderland
1-i recorded the characters using green screen, then separately their heads by covering their bodies.
2-I created layers of a scene, both background and anything i want floating in front of the character keying out anything i dont want..
3- i used Adobe premiere and places the music with the 2 beep i also recorded all the videos with the heads syncing them up, one by one i attached their bodies and nested the two videos, big heads over little bodies,
4- after creating a sequence of the scenery and music i placed the nested sequences of the heads and bodies and re sized them into the main sequence aka scene, example outside in a farm etc.
It looked better then anything i ever seen in film or TV but hey, the spherized effect failed to render, it was perfect but when trying to render it would return to its default position in the center, also my 8 point Garbage mattes would expose things i never left exposed, after rendering or exporting the video, every time i would go back to check why it will return to the state i left it which was correct but again and again the BUG with Premiere Pro continued until it crashed and corrupted the file itself so sadly i am also looking for another solution.
FCPX is a joke, UNPROFESSIONAL, no way to nest, oh wait maybe in 2015 or when a competitor who does not go to lunch or bed with the sleezy developers comes along with a better app, regardless of the frustration after buying the Adobe 6 Suite and ending up with this trash i have and will still be looking for a solution, Tricaster for mac? not sure where to start cause i did all the scenery in PS
oh well, ill prepare to bother everyone here and other forums to dig up a solution, but try Premiere pro with photoshop if your syncing with audio, maybe it will work for you cause i used a imac i7 2010