That feature is already available. In the Connect Equipment window select Simulator for your camera and On-camera for your mount. Optionally, select Simulator for your AO.
Just make sure you are using "Simulator" to get the built-in PHD camera simulator, not one of the ASCOM simulators (which all have the word "ASCOM" in them.)
The Cam Dialog works for the simulator and allows you to tweak lots of stuff.
Several people have overlooked this and asked this same question, so maybe we need to change the name from Simulator to something more explicit, like "PHD Camera Simulator".
Andy Galasso