How can I configure Adobe Audition so that it loads a specific session when it starts?

There is no command line structure for this, I'm afraid.

What most people do, if they don't use a standalone batch processor to accomplish the task, is to put the focus on the session file itself. What this means is that you have to make sure that the session file invokes Audition when you click on it:

This is inherently more powerful than altering the command line structure, because it doesn't tie Audition down to any one file. If you want it available directly from the desktop, then create a shortcut from the file in the list and put a suitable name on it. For instance, the one above now has an Audition desktop icon looking like this:

And this does exactly what you're asking for when you click on it.