The simplest way (you must use setInputReceiverEnabled (false) in this case):
ICameraSceneNode *camera;
camera = smgr->addCameraSceneNodeFPS (0, 100, 500);
camera->setInputReceiverEnabled (false);
then:
camera->setPosition (irr::core::vector3df (posx, posy, posz));
camera->setRotation (irr::core ...