How to disable access to the Exchange Admin Center from external users but still allowing the external users to access the ECP site.

Hi,

I guess that subject says it all. I'm trying to figure out how to block external users from accessing the  Exchange Admin Center but still allowing external users to access the ECP. I found some useful documentation on the net but it was not the answer I was looking for, such as:

1. Using the Powershel cmdlet which disables access from everyone.

2. Adding the "IP and Domain Restrictions" feature and allowing the company's internal network and denying the rest.  I thought this was the answer but although users are not able to access EAC from the outside they are also not able to access ECP.

Is there any workaround?

Thanks,

Phil