You raise the more generic question of how to handle multiple (and multiple kinds of) responses - one of WSDL's shortcomings.

Consider moving to a generic signature like: IMessage[ ] Execute(IMessage[ ] input);

Then consider moving to a publish/subscribe model.

Finally, you'll find that (as this post shows) you don't need any request/response semantics for getting information .

Give it a try. It's more scalable than the synchronous request/response the tools auto-magically spit out.