If the pilot is on the apron, and can see greater than the announced visibility (or different wx for that matter), surely a radio call to the tower (or ground) to get them to concur would be sufficient?
Secondly, in the US, a Pirep is legally required if the weather observed is different from published. (This is for enroute, not sure if "from the apron" qualifies for filing a pirep). This would constitute a valid legal briefing.
a) I wonder then if a pilots own Pirep would qualify as a weather observation for the intents and purpose stated in the original question and
b) if Pireps would/could work this way in other countries.