Norway is still bound with Sweden at this point. So, perhaps have Stanley get funded by the Swedish King? Really, it comes down to who funds Stanley's big trek across the Congo. Then have the Swedish government establish a colony there, with concessions to Britain in some form or another. By the time of the Berlin Conference, Sweden's mandate is approved and confirmed. It'd be helped if Sweden tried to have more prominence in world affairs, so that they'd be considered in the first place.