That is correct. There is no way, especially if the original caller is external, to send that original caller ID on the second leg of the call. The caller ID has to be part of the number range of the PRI that made the call; in your case, the Enterpri...
When subscribing to a service (via UDP, template etc), the only services you get are the ones created in Device>>Device Settings>>Phone Services.Create a new service, call it EM Service and use that for subscription.Hope this helps!!