User behavior model is now dependent on set of specific feature set, right now it is not possible to achieve this and it will require product change. I am in favor of this idea and will highly recommend that you open an Idea( Enhancement) on the communities side.
What is possible right now is that you can write a callout and get the Risk Evaluation done for the Non CA Risk server and then feed that data to CA Risk server. There is not much information available in the documentation so it has to be a services task if you want to take this route.
Thanks
Namish