there is an fx camera. you could hide the hud from the fx camera like so... (i can't test this, sorry if it doesn't work):
showentity hud
showentity camera
hideentity fxcamera
renderworld()
hideentity hud
hideentity camera
showentity fxcamera
renderworld()
showentity hud
showentity camera
hideentity fxcamera
renderworld()
hideentity hud
hideentity camera
showentity fxcamera
renderworld()