If I read you right you're saying...
(1) Estimate directional stability to determine rudder deflecton
(2) Estimate lateral stability to determine aileron deflection
(3) Calculate incremental drag due to rudder and aileron deflection
(4) Factor increase in CDo to t/o roll equation.
Ouch, I'm sure it'd be an interesting exercise, but it doesn't sound a particularly good way to get meaningful numbers - there's a lot of places for errors to creep in.
G