Workflows allow Argument definitions but not Workflow Services?

I've been working with WF 4 quite extensively the last handful of months and I've noticed that on the WF designer there is an "Argument" button you can click and then view the list and/or add additional args.

It would be real beneficial to add arguments to a WF Service but in the designer you do not have the same option. Is it possible to define arguments in the XAML or is there a certain reason why arguments are not permitted?

I want to pass in argumen开发者_如何学运维ts to a Workflow Service that I constructed with the designer. Ideally, I'd like to pass in a string argument into the WF Service from the application which is hosting it (a Win Service). The same application also hosts a Xaml Workflow which I pass in several arguments to allow the WF to do it's job while running.

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With a workflow service you start the workflow using a WCF request modeled using the Receive activity. So the Receive activity is where you want to add arguments.