Hi again,
This is beyond my expertise! I have attached some papers that could help you out. I believe that the two-tone analysis technique is required (on top of performing single tone analysis).
Here’s a link to Wikipedia which describes the process:
http://en.wikipedia.org/wiki/Second-order_intercept_point
http://en.wikipedia.org/wiki/Third-order_intercept_point
Sorry I couldn’t help further.