With British Airways flying out from Copenhagen to Los Angeles and back from Las Vegas to Dusseldorf for only €352. Bookable on the german version of Ebookers. You should search a multi city flights. Just click on ‘Mehrere Stopps’ in the search form.
Outbound: Copenhagen – Los Angeles (4 Nov.)
Inbound: Las Vegas – Dusseldorf (13 Nov.)
Just click on the image below to check the price:
From Los Angeles to Las Vegas you can book a low cost Megabus coach for only $5.
For your information: On the way back to Europe there is a stopover in London, where you can simply skip the last leg to Dusseldorf and get off the plane if you want and take an another flight from London to your home. However you have to add Dusseldorf as a final destination because this is the only way to reproduce this fare! It is not possible to skip the first leg Copenhagen – London, your ticket would be cancel then.
Ryanair flights depart from London Stansted Airport and Wizzair flights from Luton Airport not from Heathrow. You can get to Stansted Airport from London city center with Easybus for only £2.