Call this method to add a waitable object's handle to the list maintained by the worker thread.
The handle to a waitable object.
The pointer to the IWorkerThreadClient interface on the object to be called when the handle is signaled.
The parameter to be passed to IWorkerThreadClient::Execute when the handle is signaled.
IWorkerThreadClient::Execute will be called through pClient when the handle, hObject, is signaled.