Guys
I can see a possible way of keeping the western powers out, [perhaps] but it needs a slightly different POD.
I.e. Germany doesn't occupy the rump of Bohemia in spring 39. That was the thing that really killed appeasement in Britain. Instead it starts making moderate demands on Poland, i.e. Danzig and a right of passage through W Prussia to E Prussia. Possibly even Hitler asking his 'friend' Chamberlain to act as mediator.
Presuming Poland refuses to compromise Hitler has an excuse to invade. [Although then explaining his continued occupation of all Poland would be awkward without alienating the western powers]. Hitler would still have to garrison the western front to secure against an attack and would lack the loot from the west but this might give a chance of getting an eastern war only. Plus it would enable Germany to start further east, although a lot would depend on Stalin's reaction.
Alternatively Poland concedes the land, in which case either it must be overtly attacked, alienating the west. Or possibly the Polish leadership are persuaded that the western powers will desert them and take the partially less repulsive option [to the Poles at the time] of allying with Germany rather than the Soviets.
Rather an unlikely set of options but might with a small change give what the poster is after, i.e. a broad front Nazi-Soviet war without western involvement. Also if the Germans tried this and it didn't work I can't see they actually lose anything.
Steve