For others playing around with this.. The Object module has a method called exec_workflow. Signature (C#): object Execute_workflow(string db, int user, string password, string model, string signal, object id);

The trick is to find the id of the correct signal to call.. but Workflows -> Transitions is a good place to start the hunt.

If anybody else has the need to communicate with an Odoo using C# .NET, then contact me.. I am building a library to streamline this for you.