Those instructions are a bit over my head.  

Are you sure it is possible to sign the transaction using the command line when the private keys are stored in a Ledger Nano?

Edit:  When I tried entering "cat unsigned.txn | electrum signtransaction - > signed.txn" in the Windows Command Prompt window, it did not recognize "cat" as a command.  Is there some other place where the command should be entered?