Just have the Enterprise fall into a black hole or vortex of some kind and emerge a long time ago in a galaxy far, far away.
In fact, that works for just about any crossover you can think of.
But, again, what would be the real point? The story will be moving way further from Earth human-centered stories (ST's focus) and further from internal power struggles in a well-established political structure (SW's focus).
Sounds like the worst of both worlds to me.
The point would be the same as any crossover - to have the characters meet. Trek and Wars aren't about "internal power struggles" or whatever the hype says, they're about characters
. The people that inhabit the universes and make them entertaining. Only the technical fanboys care about whether a Star Destroyer could defeat the Enterprise. Most people would want to see Han Solo meet James Kirk or Spock have a conversation with Yoda. Just like they wanted to see Iron Man meet Captain America or Thor.