Liam, generally speaking most teams that I have worked with on the night shifts (covering the period 11.30pm to 12.45am tend to put all (well, most) of the freighters on the North runway, particularly if there are a few departures on the South...which there normally are. One night recently an irateish A300-600 freighter Captain rang the tower to complain about being put on the North runway during that period and said that we (ATC) were just being lazy!!!!! So it just goes to show! He also stupidly said that "this girl" (female ATCO) is always doing this...considering that we have probably 50 females rated as tower controllers, his voice recognition must be pretty good.
The normal way in which the South runway is offered is that the Tower South controller(118.4) will try to forecast ahead when there will be light(ish) departures, he/she will then advise the APP people that the South is available for XXXX, the people in the centre will have a think about it, and then will revert back to the tower in agreement or otherwise. At some point during the latter part of this decision making proccess the offer will be made to the aircraft concerned. This will normally only happen approximately 8 to 10 minutes before touchdown. In addition, during periods of heavy arrival traffic, then the APP people can dictate to the tower that the South runway will be used for a given number of arrivals.
Give my regards to Noel!