The easiest way to do this is to create an IP phone service that points at the remote directory. To do this, create a phone service under Feature-Cisco IP Phone Service using the remote directory URL. This should be :
http://remote_server_address/CCMCIP/xmldirectory.asp
Subscribe phones to this service (or have them subscribe through user pages) and they can hit the services button and then select whatever you called this service, then conduct their search.
If you want all to appear under the Directories button then you have to create your own web page(s) for the Directories URL, which is more involved. You'd have to create your own page, have the xmldirectory.asp functionality included, along with the remote directory, and assign it as your Directories URL in Enterprise Parameters. Not horribly difficult, I don't think, for someone familiar with creating web pages/scripts, but not something I've done before.
