Ok, just before the war, Germany changes its war plans to be able to wait a week after mobilization before launching a west front attack through Belgium (concern over British sensibilities about Belgium), recently completed fortifications in the Masurian lakes area, and the overall rational need to play politics for a week before launching a world war make this all possible to consider this. Plus the navy and colonial office want the extra week to fit out some raiders and ship stuff out to the colonies, gather up some merchants to send home and crash import some stuff. Germany DOWs Russia as part of the diplomatic escalation, but does not DOW France.
France DOWs Germany.
Britain initially neutral hoping to avoid war, still negotiating with Germany over Serbia, but mobilizes her fleet.
France misreads German intentions, that the Germans want to strike east, start pressuring the Belgian government to allow French armies east of the Meuse. The British government backs this and applies diplomatic pressure on the Belgians to allows this. The Belgians protest but allow this. The French move across. This triggers a German reaction, Germany DOWs Belgium, and the Germans launch their attack, sort of OTL like.
This turn of events backfires in the British cabinet. Germany and Britain had been working up a peace deal in Serbia but that is forlorn now. France actually invaded Belgium first and anti war sentiment breaks out. Germany makes some smart diplomatic pledges about what she wants out of the war and does diplomacy well for a change, Britain hesitates....