Have long-term German planning supporting anti-colonial uprisings in the British & French empires; extra points for the Second Indian Mutiny.
With problems for the French especially in Indochina, perhaps the Japanese will bat for the Central Powers, which might drag the Americans in (& perhaps the Dutch). We will certainly make it a bigger conflict if we can get the Chinese involved, so hopefully Japan's appetite just peaks a couple of years early.
Speaking of the Dutch, the Schleiffen Plan involves sweeping through the Maastricht Appendix, which the Dutch chose to interpret as an act of war. Or the British elect to turn the German right flank with an amphibious landing in the Frisian Islands
Switzerland on the map appears to be a good route to outflank the Western Front. All you need is a general staff that can't figure out what all those brown lines on a map represent.
The madness of Admiral Essen has already been mentioned so the Swedes are spoken for; Denmark is a nice place for the British to land on (they may not all get off the beaches though) so the Germans may pre-empt the invasion - it's just a question of dates as far as the hapless Danes are concerned.
The Portuguese (or their ever shifting governments) were pretty desperate to enter the war just in case their colonies were used to buy peace so they can make it under their own steam. Spain is a bit of a problem as I can't see them fighting unless the Central Powers are on the verge of victory.
Ideally either Britain or Germany has long standing plans to distract the Americans by inducing Mexico to commit national suicide (although the presidents will be nice & rich in exile). After that setting the fratricidal South Americans at each others' throats would be child's play.
Struggling to spread the war to Antarctica unless the followers of Scott & Amundsen decide to settle matters of honour on the ice shelf