ODBC Driver for Salesforce: Access Linked Server Object in SSMS
I'm going to take a chance and suggest an answer but in this case without the specific product and setup, of course I'm unable to verify.  I believe what you will need to do is go into the Security settings of the Linked Server and specify a particular account to use to make the connection.  That is, create an account on the server you want to connect to, like SalesForceReader, with the corresponding privileges needed, and use that account and password in your Linked Server.