For some reason the Citrix eDocs section for Receiver Enterprise 3.4 does not contain information about how to deploy Citrix Receiver with a Pre-configured PNAgent / Online Plug-in / XenApp Service URL.
In Receiver 3.2 it was possible to use the SERVER_LOCATION= to specify your XenApp Service site URL, if you take the Citrix Documentation at face value, this switch is no longer available. But if you run CitrixReceiverEnterprise /? at a command line you will see that this installation switch is still available.
I found out this information in some posts deep in the Citrix forums but it took me a good while of testing and searching to find them. So I am hoping by blogging it I will make someone else life a bit easier.