Note that mstsc.exe has no (documented) options to supply a session ID.
But once you have logged in to the Remote Desktop Session server, you can change the session you are connected to by issuing
tscon <session id> /v
See MS KB 321703 for details on tscon.
Alternatively, you might use tsadmin.msc and the “Connect” function from the context menu of the “Sessions” tab:
As another idea, you could try supplying an alternate shell with the RDP configuration file which would run tscon <sessionID>, but I am not quite sure it would really pan out as you intend it to.