A young, newly checked out local controller at Logan Airport granted the request of a Trans Portuguese "707" to use non-active 15R (the longest runway) for departure and cleared the plane to "taxi into position and hold". Seeing what he thought was a short pause coming in crossing operations, he told the crew to "Be ready and spool 'em up!" The old "oil burner" sat on the runway with fire walled engines belching clouds of black smoke over nearby neighborhoods for many minutes. Only when the ground controller announced that airport fire apparatus was responding to a major fire in East Boston did anyone in the tower realize that the rookie (now stirring his newly poured coffee) had forgotten the plane and everything from Orient Heights to the Mystic River Bridge had disappeared in his exhaust. (Ack 'a former ATC')