Question About Sejuani Rework

So in the announcement it specified that both Sejuani and her melee allies can begin smacking away at enemies to apply Permafrost. Being melee only obviously adds strategic value.

But once the Permafrost is applied, can ranged allies also stack it?

So say there's a bot lane of Ezreal and Nami. Obviously they can't start stacking Permafrost on their own. But once Sejuani gets into melee range and applies the first instance of Permafrost, will their basic attacks then contribute to the stacking? Or is it still melee only?