Alembic route is most likely the only way with read from file. It’ll be brutal I’d imagine. There are no VDB tools in Flame… there’s Eddy for Nuke but that’s more about fog volumes than sdfs that one would surface.
I’d imagine the other alternative would be faking refraction in Flame/Comp via normals and some other aov’s you could render in RS alongside the bty.
Sorry it’s not a better response.