Need help tying in a backstory to Reign of Winter

Take a look at book 4, the adventure moves to Triaxus, a neighbouring planet. You might find your inspiration there

Some thoughts:

• There’s planet-hopping later.
• You could talk up the ley lines as constellation maps, sooner.
• I vaguely recall Norns in the last book, and if there aren’t already then they would totally fit - so you could tell a story about ley lines, constellations, and woven skeins of fate.

There's a forest in the Lands of the Linnorm Kings that's just over the border with Irrisen. It's got numerous gnome settlements and is riddled with portals to the fey First World, which could explain part of their walkabout. There's even a town of Irriseni refugees and two deeply weird fey settlements, as well as the home of the feylike Father of All Linnorms, Fafnheir. Other planets and the First World come up a lot in the later books, which should be fun for that character. Were they a part of the party from the first session? Maybe stories of anomalous winter drew them to Taldor in hopes of finding a weird portal? That way you could have both a connection to Irrisen and Taldor without making them an Irrisen native.

There are other gnome settlements throughout the continent, many of them in weird spots like Grungir that have connections to the fey realm. There are whole settlements of cold fey in Irrisen too, it wouldn't be hard to imagine running into a relative, friend, or like-minded gnome traveler in Irrisen. Given the "walkabout to the stars" nature of his people, you could put somebody from his tribe almost anywhere in the story. Perhaps he has an aunt who got stuck on Triaxus decades ago or a distant member of the tribe who got trapped in the Dancing Hut itself!