Posting this for people to confirm, but i had my friends guild try it as well (25m H Rag).
While the Magma trap is spawning (the swirling animation), have a rogue throw a smoke bomb right on top of the area it is spawning on. this will cancel the trap and no trap will spawn.
this is extremely useful to avoid damage from multiple traps during the encounter. it is only limited by the rogues CD and the amount of rogues (no rogues in our raid currently tonight, but friend confirmed both of his rogues using it in P1 attempts to cancel out two traps).
enjoy your healers not having to heal 25 people!