Britain and France commit troops to Poland itself to help hold off the German invasion, as soon as possible after the invasion begins.
How exactly do they get there? The most direct route would be via the Baltic but I think the
Kriegsmarine and
Luftwaffe might have had something to say about that. The only other ways are overland via Italy, which as a quasi-ally of Germany I doubt would grant transit rights, and then other countries or via the Mediterranean and Black Sea which would take much longer and then still need transit through either Romania or the Soviet Union which I can't really see being forthcoming.
A larger Saar offensive, in which the French military succeeds in launching its 40-division assault and isn't quite so half-hearted.
The problem with this if I remember correctly from previous threads is the way that the French army was structured - to launch a major offensive would require them to call up their reserves but the way that was organised it took a lot of time and effort, which by the time it would have been completed Poland was already doomed. The British weren't much better since the army had always been at the back of the queue for funding behind the Royal Navy and Royal Air Force so plans for a 'continental force' that could intervene on, as the name would imply, the continent had to be continually scaled back and eventually effectively cancelled. They also had the problem of having to deploy first across the Channel to France and then move up to the border for an assault into Germany.
If you want it to be possible then I think you would need to make some rather larger changes to how things were set up with the French and British militaries. Which then brings up the question of if the Germans know that they can now mobilise faster would they still risk an attack on Poland, or if they do will they have to weaken it by leaving troops on their western border to the possible extent of undermining the invasion of Poland itself which is the whole point of the exercise?