Pass parameters while creating a WCF Service Host

Question

I have a WCF service -

public class DemoClass : IDemoClass
{

}

I can successfully host this WCF Service in another managed windows service. When the main service loads I start my WCF main service like this -

ServiceHost servHost = new ServiceHost(typeof(DemoClass));
servHost.Open();

I now want to be able to pass parameters to the WCF service when it starts so that I can pass something to it's constructor -

public class DemoClass
{        
   public DemoClass(string parameter)
   {
       //need to access the parameter value that is passed here.
   }
}

ServiceHost does not allow me to do that. How can I achieve this?