I figured this out quit a wile ago, sorry it took so long to get the answer posted.
Create a separate service contract called IDefaultDocumentService with one method on it that is decorated with both OperationContract and WebGet.
<OperationContract(), WebGet()>
Function GetDefaultDocument() As System.ServiceModel.Channels.Message
Now implement that contact in a very simple DefaultDocumentService class
Public Class DefaultDocumentService
Implements IDefaultDocumentService
Public Function GetDefaultDoc() As Message Implements IDefaultDocumentService.GetDefaultDocument
Return Message.CreateMessage(MessageVersion.None, "", "Hello!")
End Function
End Class
In the config file for you windows service hook up a separate service for the DefaultDocumentService and map it to the root directory of your other WCF service. When you are putting these services into a Web Farm on ISA it will hit your default document service and get a "Hello!" message which is enough for the ISA server to know that the service is alive.
<system.serviceModel>
<services>
<service name="YourMainService">
<endpoint address="http://localhost:10000/YourMainService.svc"
binding="wsHttpBinding"
contract="IYourMainService" />
</service>
<service name="DefaultDocumentService">
<endpoint address="http://localhost:10000/"
binding="webHttpBinding"
behaviorConfiguration="DefaultDocumentEndpointBehavior"
contract="IDefaultDocumentService" />
</service>
</services>
<behaviors>
<endpointBehaviors>
<behavior name="DefaultDocumentEndpointBehavior">
<webHttp/>
</behavior>
</endpointBehaviors>
</behaviors>
</system.serviceModel>