The easiest way to do this would be with a scan tool or computer software that can access the stability control system of the vehicle and then datalog the steering wheel angle.
You might also be able to use some sort of logic analyzer to analyze the bit stream, but finding the protocol and bus detail for the specific vehicle you're working with could be tricky.
Another option would be to tap in to the sensor wiring with a buffered datalogger and pull off the information you are looking for. The sensor is likely either a hall effect sensor or optical rotary encoder and it would be relatively easy to calculate by monitoring the bit stream while turning the steering wheel from lock to lock slowly.
-Rod