Unfortunately that's not possible with the current setup. The "Disable Native Spawning" toggle is all-or-nothing. it blocks all ore types (stone, metal, sulfur) at once.
Your options right now:
Closest to what you want: Turn Disable Native Spawning OFF, enable only Sulfur in the plugin, and tweak the biome probabilities down to reduce it. Stone and metal stay fully vanilla. The downside is sulfur will get vanilla spawns plus plugin spawns stacked on top, so it might not reduce it as much as you'd like — it'd actually increase it.
Full control route: Keep Disable Native Spawning ON, enable all three ores, and just set stone/metal to roughly match vanilla defaults while tuning sulfur down. Not truly vanilla for stone/metal but you get full control.
Neither is a perfect solution for your use case. I'd suggest leaving a new feature request