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