I don't think this is possible. However, I would be happy to look at your configuration and the output from a debug voice verbose and debug sip stack messages when you attempt this, if you can upload them to our FTP server from the instructions below.
Open Internet Explorer web browser on their PC
Type the following URL: ftp://ftp.adtran.com
Press the Alt key, click View, and then click Open FTP Site in Windows Explorer
Double-click the "Incoming" folder
Drag and drop files from PC into the Internet Explorer window
Reply to this post with the exact filenames used so we can retrieve the files
It is not quite the same application, but here is a related post about picking up remote analog calls: Spre code to pickup analog phone line individuals
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