After doing some research, I think I have a answer to my own question:
Long Answer
A WBO2 sensor doesn't care what the fuel is, gas, methanol, propane, etc.
It measures the ratio of oxygen left in the unburnt gases exiting the engine; in essence measuring true Lambda instead of Air/Fuel Ratio. The sensor output is then calibrated for AFR based on which fuel is burnt. When replacing fuel with another fuel type, like when injecting water/MeOH, thinking in terms of AFR will not make sense because of the the different stoichiometry of the fuels.
The magical number for turbo gasoline cars is 12.5:1, which works out to around 0.85 Lambda. Now when injecting MeOH, you should still shoot for this target. Including the MeOH, the target fueling should be 15% rich.
Short Answer
Inject MeOH, try to hit target AFR of 12.5 based on WBO2, back off a little at knock.
Sources
Methanol Injection Dilemmas
Gasoline, Methanol, AFR, Lambda, and Stoichiometry.