D&D 5e has a new D&D concept called Bonds. Bonds are pieces of your background that tie you to the campaign world. These can either be connections to NPCs, or a homeland, or even a particular weapon or item in the world.

The group I'm currently DMing for, has had characters wandering from the 10 towns in Icewind dale, to Dragonspear castle, to some unnamed forest, all in search for gold and glory, and have now found themselves in the grassy plains near Greenest about to start the Hoard of the Dragon Queen for the Tyranny of Dragons story arc. The characters are level 3 and have been played for about 10 1 hour sessions so far. (One character is preaching the gospel of the divine turnip, one is an ex-slave blacksmith turned monk, and the other is an herbalist looking to heal the world, or "smoke it" trying.)

I'm very excited about the idea that each major module comes with some bonds for players to pick (or roll) to tie characters more closely to the module, making the adventure more personal. However, since we are not starting at level 1, I'm unsure how to add the provided bonds without some cliched 'it was all just a dream', 'hand wave', or 'repressed memory'. I'd like to get advice on what works best in adding background history to characters who are a bit more established than you would otherwise assume.

Below are the suggested bonds, so you can get an idea of what sort of connections are suggested:

The list of Bonds (chosen with a d10)

1. Leosin Erlanthar, a wandering monk once saved your life. He's sent an urgent summons for you to meet him in a small town called Greenest. Looks like it's time to pay off that debt.
2. When an orc raid drove your family from your home, the people of Greenest took you in. Anyone who threatens Greenest is your sworn enemy.
3. Every five nights, you have a strange sequence of apocalyptic dreams. The world is destroyed by cold, choking fumes, lightning storms, waves of acid, and horrible fire. Each time the dream ends with ten evil eyes glaring at your from the darkness. You fell a strange compulsion to travel to Greenest. Perhaps the answer to the riddle of your dreams awaits you there.
4. Ontharr Frume, a crusading warrior and champion of good, is your frient and mentor. He has asked you to travel to Greenest in search of rumors of increasing dragon activity.
5. You have heard rumors that your close childhood friend, a half-elf named Talis, has been kidnapped by a strange group of dragon cultists. Your investigations into the cult have led you to the town of Greenest. You must save her!
6. Being the grandchild of a renowned dragonslayer is usually a good way to impress people, but just last week a gang of ruffians attacked you. You barely escaped with your life, but as you fled the ruffians told you that the Cult of the Dragon never forgets and always avenges. You're hoping to lie low in a sleepy little town called Greenest, until this blows over.
7. On his death bed, your father confessed that he had been involved in a group called the Cult of the Dragon. They paid him to smuggle goods across the Sword Coast. Wracked by guilt, he begged you to investigate the cult and undo the evil he may have helped foster. He urged you to begin your search in a town called Greenest.
8. The dragons destroyed everything you hold dear. They killed your family and destroyed your home. Now, with nothing but what you carry on your back and a horrid scar of the near fatal wounds you sustained in the attack, you seek revenge.
9. You and your family were members of the Cult of the Dragon until your rivals in the cult arranged to wipe you out. Though they slaughtered your kin, you survived, but they think you are dead. Now is your chance for vengeance! Your hit list consists of three names: a human cultist named Frulam Mondath, a half-orc named Bog Luck, and a half-dragon named Rezmir. You have arrived in Greenest knowing it's next on the cult's list of targets.
10. You have a secret. You were once a gold dragon who served Bahamut. You were too proud and vain, to the point where Bahamut decided to teach you a lesson. You have been trapped in a weak, humanoid body, with your memories of your former life but a dim shadow. You remember only one thing with clarity: Bahamut's command to go into the world and prove your devotion to the cause of good. If you prove worthy, on your death, you will return to his side in your true form.

How can I best introduce these new bonds to the players?