As far as we know, the Link itself could create the illusion of the planet having a warm surface. Even a single adult Founder has great powers over its environment, sometimes shrugging off phaser blasts like in "Heart of Stone", sometimes roaring like a wall of flame like in "Chimera". And we never quite learn what a Founder requires of the environment in return. Possibly next to nothing, considering the backstory of Odo wandering through space in his youth, the more expository version of Laas actively flying through space, or the infant from "The Begotten" surviving in a simplistic-looking little canister.
Timo Saloniemi