How do we specify a state-dependent roughness length?

[glwagner]

The COARE 3.0 algorithm for air-sea fluxes uses a state-dependent parameterization for the roughness length over open ocean (Fairall et al 2003, equation 6):

This can be thought of as a crude parameterization for the effect of the equilibrium surface wave spectrum on the effective roughness length that applies in a bulk formula framework for air-sea momentum fluxes. See also Edson et al 2013.

If it's possible to specify this now, I don't know how (for example, nowhere do we specify the kinematic viscosity of air, or the two free parameters that enter into this roughness length parameterization). If it is not possible to use a state dependent roughness length perhaps some pointers would be helpful on how to generalize the code to allow this.