During these 3 years Germany will become a lot stronger and demand a lot of land saying "ThErE aRe EtHnIc GeRmAnS liViNg ThErE. " dont stop it. Let germany annex all the Land they want to, after all you dont want to risk war, you are trying to keep the fragile peace of world war 1.

but you can try and keep the peace by guaranteeing countries like Poland, this will give them a false sence of Security and they will not give in to Germanys demands since they think you are backing them. Also you should join the allies during this period, since you need someone to free help you anyway.

The Situation is: you have joined The allies, you and Britain are guaranteeing Poland, and Germany sent poland an ultimatum about danzig.

you need to tell Poland you will support them, this will cuase them to decline the Ultimatum and start a war. You and the rest of the allies will join the war, and wait. You should move all your troops to the Maginot Line since Germany would never attack trough Belgium. after a short bit Poland should surrender, keep Doing nothing.

Sometime in early 1940 Germany will attack Denmark and Norway, you dont need to care about it, Britain has the Navy, not you. Next Germany will attack you, if they try to go through Belgium (which is highly unlikley) then dont stop them, hold the Maginot Line. If everything goes well you should surrender in at most 2 months.

During this time you wont be able to do much, you will be fully occupied by Germany and the only land you have left is Africa. Dont use your remaining ships and units, let them sit around.

in 1944 The allies will do the D-Day landings and invade Normandy, from there on they will free you. once they have capured paris you will once again be able to join the fight, But dont. let them do it all.

Then once Germany surrenders you can act like one of the big players, without actually participating in the War.