Well first you need a reason to have the Germans move into Switzerland. How about this- after Ausschluss and Sudentenland, Hitler, in perhaps a moment of madness, decides he needs to Ausschluss Denmark, The Netherlands, and German Switzerland, as to create a pan-Germanic State, putting his Poland Plans on the backburner for the meantime. Now of course, he needs someone on his side, so lets say Italy. He has Operation Christmas Tree planned up, and makes an agreement with Mussolini to invade and divide Switzerland, not considering the Swiss battleplan and expecting a full on war. Now let's say Mussolini, in a moment of clarity, tells Hitler to sit on a long pole- okay, Hitler is pissed, but decides to go ahead anyway, getting a hard on for the idea of a new Holy Roman Empire, upon which he can launch Lebensraum. He Invades Switzerland, only for the Heer to find the Swiss retreating into the mountains. Hitler annexes the German speaking regions, and turns the rest into Protectorate. However, he faces a Partisan War that diverts his attention from the rest of his Ausschluss plan, with the Italians and French supporting the rebels. Of course, this will not do, so Hitler launches a Blitz through the low lands and France, and attacks Italy through the Alps. Both are, however, able to hold off better as they've been anticipating an attack, and turn the front lines into meat grinders, although end up overrun anyway. Pinned down in now France and Italy as well, Hitler now fights off a coalition of Britain and Poland, who attack the bogged down Germany. Economy collapses overnight, and Hitler is deposed of in a Military Coup.
I admit that's not the most realistic, but its the first one I could come up with off the top of my head.