Grails create instance of inner class of service

In Grails, services are singletons by default. Can I keep it that way and still create an instance of an inner class of that service from a controller?

//by default grails makes MyTestService a singlton
class MyTestService{

     public class InnerTest{
          String msg;
          def addMsg(String str){
               this.msg=str;
          }
          def printMsg(){
             println this.msg;
         }
     }

}

In controller "MyController"...

def m=myTestService.getInstance().new InnerTest();
//produces " MyTestService.InnerTest cannot be cast to MyTestService.InnerTest"

 def m=myTestService.new InnerTest();
//No signature of method:MyController.InnerTest() 

You should be able to do something like:

class MyTestService{

     public class InnerTest{
          String msg;
          def addMsg(String str){
               this.msg=str;
          }
          def printMsg(){
             println this.msg;
         }
     }

     def InnerTestFactory() {
        new InnerTest()
     }

}

And use it from your controller:

def m=myTestService.InnerTestFactory();