Getting Switzerland to be invaded is common and (more or less) easy in the 20th century.
But your challenge is now to have Switzerland start a war and be the aggressor party in a war. It can win or lose, expand or get partitioned, but Switzerland (or Liechtenstein) must have been the aggressor party, i.e. the first country to declare war on somebody else and/or the first country to fire shots.
In such a war, Switzerland is allowed to have allies, but they must join at some later point...