There is always a starting point where everybody will begin the adventure. I do not know of a work-around for that. The Undermountain Project is the same. Everybody has to start in the tavern, and grab a pass to be able to enter the door that leads to Undermountain's caverns. In order to meet up with people, you gotta run to catch up, make them wait on you, or have a planned time to meet at the start point.
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