I remember early on that I was having the same issue. After some experimentation, I came up with what I think is a good way to train the ECU. I can usually get the OAR to snap to -1.00 within two or three runs.
1. Drive until the engine oil is fully warmed up, and then find a long stretch of road with very little traffic.
2. Bring the vehicle speed up to around 25 MPH, and then shift into 5th gear.
3. Start accelerating while at first being very, very, very light on the gas.
4. As the vehicle speed increases, give it more gas. The idea here is to maintain a constant load on the engine by smoothly and linearly increasing pedal input as the vehicle speed increases. I've gotten the best results by maintaining a very light load. That's why I recommend starting out very light on the gas.
5. Continue increasing pedal input until the vehicle speed is around 75 or 80 MPH. If the OAR hasn't reached -1.00, do another run.