I'm going to describe better my idea to see if i understand it better...
The canceling self induction is accomplished by having the coils exactly the same size and perfect coupled.
Resistance of the wires distance and gaps between the coils can help reduce the coupling. Reducing the coupling makes the coils acts like inductors again but coupled to each other to some degree.
This is the key.
I thin the best design would be each inductor wound in a of a C core and the other on the other C core so the coils can have a gap between each other and this way the coupling can be perfectly adjusted.
The Dc current in the secondary completely cancel out its magnetic field since is applied thru the central tap so it does not interfere nor saturate the core induction capabilities while if they are are at different portions of the core two regions of bucking magnetic fields is going to be created that might interact with primary magnetic field.
A magnetic shunt could also be used to try to decouple the coils or the secondary from the primary. it could be a good idea.
an inductor store energy in the form of magnetic field when there is current flowing in it. My idea is that the stray magnetic field of the dc current on the chokes will help decoupling them therefore increasing the induction somehow.
I also thought of other possibility of having two CC cores each with its choke, and to provide a coil that is shorted to its self and passes thru both cores... this way they could be maybe changed the game. I have to think about.
Illustration of the concept (http://www.ionizationx.com/index.php?action=dlattach;topic=2863.0;attach=13412;image)
(http://www.ionizationx.com/index.php?action=dlattach;topic=2863.0;attach=13414;image)