Thanks again for pointing me in right direction... all sorted! 
All done in C#
I connect direct to the new host using System.Net.WebClient and download the default SSL cert from host/ssl_cert
Then read file into byte stream and process using System.Security.Cryptography.X509Certificates.X509Certtifcate2 to get at the thumbprint.
Finally split up into pairs with : in between (took me a few moments of wondering why still not working until looked up HostConnectSpec!)
Then host added.. at last!!!
