To push his nose past the judges' box

"I realized exactly what must be done if this Fink-Nottle was to be enabled to push his nose past the judges' box."
(PG Wodehouse, of coures :-) )

(It means more or less that Fink-Nottle will have the courage to do something)

What is the origin of this phrase?

Almost certainly from horse racing prior to the development of photo-finish technology. Judges had to decide which horse had won a race. Their judging point seems to have been a box on the finishing line.