There is a work-around method, but not 100% accuracy, and both servers need to be in same DF server group

Method 1, fresh party:
Player1 is a popular role (DD), Player2 is the least popular role (lets say tank).
1. Player 1 queues for a dungeon.
2. Player 1 waits for when only the player 2 role is left to fill. Duty finder shows: Tank 0/1, Healer 1/1, DPS 2/2.
3. Player 1 informs player 2 and player 2 jumps into queue.
4. If both players have matchmaking announcment, they are together.

Method 2, join in progress:
Player 1 is playing an instance where a player has left, and Player 2 plays the role that left.
1. Player 2 joins the dungeon with "join party in progress" enabled.

Method 2 is confirmed, although i used it to join FC mate that had someone left.