Considering the lag factor on our radar information (ie. the altitude we have displayed is usually a few hundred feet behind what the aircraft is really at if they are on a fast descent or climb) we could quite easily make the situation worse by issuing a vertical avoiding instruction. So I agree with the guys who said a hard turn to both aircraft is all we can do (and cross our fingers and toes). Although have to admit that not having been in that situation I really don't know what I would do until it happened (and I sincerely hope it never does). It would be easy to throw everything at it, ie. climb/descend/turn left/turn right/ traffic is etc etc etc.