Have you checked BA? They offer sensible one-way fares (usually) although you won't get lounge access of course. You will get food and booze, though, and T5 is not a bad experience these days.
Have you looked as SAS from London City? 10.10 or 18.15 departures. Depending on where you work it may be convenient - I took this when I last did an ex-CPH.