Acquire two hideaways. Then, send a letter to an officer from one hideaway, and travel to the second hideaway. Once you open the door to the hideaway, the officer will spawn next to the building outside. Simply talk with the officer to raise their bond level. Next, send a letter to an officer from the second hideaway, and return to the first hideaway. Repeat this process as many times as desired. Travel to major cities after each chapter so you avoid missing opportunities to speak with certain officers whom may be killed later in the game. This also helps with getting "The Ties That Bind Us" achievement.