First, is it plausible that through some diplomatic rangling similar to Bismark's effort with the French in 1870, that the Fuhrerreich is able to get Poland to declare war on Germany instead of the other way around in 1939?
If so, what could be done to cause it and what would be the repercussions if it occured? I'm assuming France and Britian couldn't honor their defense agreement.
Maybe a suprise Polish offensive into Silesia or recently occupied Bohemia could catch Hitler by suprise.
And off the top of my head, maybe if the Germans moved to blockade Danzig or possibly some other minor move that gave Poland enough of a Casus Belli, she may have done it