This is actually two gizmos that allow you to perform multi-plane depth of field focus pulling cheats without painful hand animation...

moggaDFchild.gizmo & moggaDFmaster

1) Attach the moggaDFchild gizmos to all the different layers you want to defocus... set the relative z-depth accordingly... if you're tricky you could drive this with a chan file possibly?

2) Create one moggaDFmaster gizmo node... don't rename it as the expressions rely on it's name... change the focal plane and defocus size as you like...
***if you don't want to take all the time to look at your comp... look at the output of this node with a viewer to approximate animation...***

here's a sample menu.tcl entry...

menu "mogga/DF Focus Puller/DF Child"                {moggaDFchild -New {}}
menu "mogga/DF Focus Puller/DF Master"            {moggaDFmaster -New {}}

Enjoy!