Configure SQL Server to associate a user login with a specific port
See the instructions at: 

Configure the Database Engine to Listen on Multiple TCP Ports

To set up a new TDS endpoint a code sample is:

USE master;
GO
CREATE ENDPOINT [CustomConnection]
STATE = STARTED
AS TCP
   (LISTENER_PORT = 1500, LISTENER_IP =ALL)
FOR TSQL() ;
GO


The side-effect of creating a Custom Connection is that you will need to reestablish the Default Connection:

GRANT CONNECT ON ENDPOINT::[TSQL Default TCP] to [public]; 


Then to grant access to the CustomConnection endpoint to the SQLSupport group (as an example), you could use something like this: 

GRANT CONNECT ON ENDPOINT::[CustomConnection] to [corp\SQLSupport] ;
GO


Read the other details in that post that may need configuring.