You would need to rig and animate the flames on the model and export it as a xfile right now.
Fbx import may or may not work for bone animated skinned meshes.
Decals work decent for such tasks and are a lot easier on the engine.
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit, Screen resolution 1680 x 1050.