Setting connection properties (application_name) for Postgres connections
If you can't configure it via the DSN itself, you can always have your connection establishing subroutine set the application name by executing a SQL command on the connection before it hands that connection back to the caller:

set application_name to 'my application name';


In VBScript, this looks like

dim cn 
set cn = CreateObject("ADODB.Connection") 
cn.ConnectionString = "DSN=PostgreSQL35WDsnHere" 
cn.open 
cn.execute("set application_name to 'my_application_name';")