I'm not sure it is an option on the 77F, certainly wasn't installed on the ones I worked on.
The nose-gear sensor a previous poster referred to is, to my knowledge, only there to provide a tipping alarm. Once it sets off it will, besides giving an aural warning, disable the CLS on the main-deck.
However, I think it needs to be established that even the system found on the 747 is not a WBS. It's 'only' there to make a cross-check with against the load-sheet, albeit it is a very valuable tool.