Implementation B.C. as a second-order derivative of another variable
 

I am implementing new turbulence model in OpenFOAM. For some models, the value of epsilon at the wall is related to second-order derivative of turb. kinetic energy (k). Any one has an idea how can I implement this kind of B.C. ?

Now I know I can get the value at the cell in the neighbor of the wall. But how can I get another cell further into the flow?

Any suggestion will appreciated. Thanks.

Jin