I got my hands on 07 Yaris steering column with ECU non-ABS ($36 ! ). I already had a pulse generator with flashing LED with variable duty cycle and I was able to actuate the ECU. The Yaris EPS is much smaller compared to Prius which is fine if you are using manual steering box. I used to be a steering engineer at Ford and I can tell you that the load rating for Yaris would be too small to be used with Rack & Pinion in a bigger car. I have converted a Cavalier Rack to manual for my Falcon. The good news is that the ECU for Yaris works with Prius EPS because both uses same torque sensor. The Yaris ECU works instantly as soon as it sees couple of pulses even if the pulse generator is removed afterwards.
According the Prius EPS troubleshooting guide, if the steering ECU sees CAN bus malfunction (like broken communication), Amount of power assist is fixed for a speed of 43 mph (70 km/h). I assume this means that what ever assist level that is provided when everything is working fine at 43 mph. Typically at 43 mph, there would be very little assist needed. Therefore, I am thinking that the steering assist will be very low when the car is not moving.
I did an un-scientific bench test with Yaris ECU (with flashing LED) and Prius ECU. I held the motor down by hand with the output shaft locked in vice with another person moving the input shaft with a vice grip pliers. Both the Yaris and Prius did not feel any different in terms of how much force I had to apply to hold the motor down.
I hope to test the entire system this weekend with both Yaris and Prius ECU.