public class EndpointSpyBehavior : IEndpointBehavior
{
    public static List<Uri> Endpoints = new List<Uri>();

    public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)
    {
        EndpointSpyBehavior.Endpoints.Add(endpoint.Address.Uri);
    }

    public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
    {
    }

    public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
    {
    }

    public void Validate(ServiceEndpoint endpoint)
    {
    }
}

public class EndpointSpyBehaviorExtensionElement : BehaviorExtensionElement
{

    public override Type BehaviorType
    {
        get { return typeof(EndpointSpyBehavior); }
    }

    protected override object CreateBehavior()
    {
        return new EndpointSpyBehavior();
    }
}

<configuration>
    <system.serviceModel>
        <behaviors>
            <endpointBehaviors>
                <behavior>
                    <mySpy/>
                </behavior>
            </endpointBehaviors>
        </behaviors>
        <extensions>
            <behaviorExtensions>
                <add name="mySpy"
                     type="WcfExtending.EndpointSpyBehaviorExtensionElement, WcfExtending"/>
            </behaviorExtensions>
        </extensions>
    </system.serviceModel>
</configuration>

static void Main(string[] args)
{
    var serviceHost = new ServiceHost(typeof(Service), new Uri("http://localhost:13056"));
    var serviceHost2 = new ServiceHost(typeof(Service), new Uri("http://localhost:15401"));
    serviceHost.Open();
    serviceHost2.Open();

    EndpointSpyBehavior.Endpoints.ForEach(u => Console.WriteLine(u));

    Console.ReadLine();

    serviceHost.Close();
    serviceHost2.Close();
}

<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.7.2" />
    </startup>
    <system.serviceModel>
        <services>
            <service name="WcfExtending.Service">
                <endpoint behaviorConfiguration="VVV"
                          binding="basicHttpBinding" 
                          address="http://localhost:1300"
                          contract="WcfExtending.Service"
                          >
                </endpoint>
            </service>
        </services>
        <behaviors>
            <endpointBehaviors>
                <behavior name="VVV"/>
                <behavior>
                    <mySpy/>
                </behavior>
            </endpointBehaviors>
        </behaviors>
        <extensions>
            <behaviorExtensions>
                <add name="mySpy"
                     type="WcfExtending.EndpointSpyBehaviorExtensionElement, WcfExtending"/>
            </behaviorExtensions>
        </extensions>
    </system.serviceModel>
</configuration>