No ~ 'stick it up your jumper' [with or without its preceding 'Umpahs'] has always been understood here to be a minced form of 'stick it up your arse' ~ as in the old music hall exchange,

"How do you make a Maltese cross with one match?"

"I don't know ~ how do you make a Maltese cross with one match?"

"Light it and stick it up his jumper!"

"I do not wish to know that ~ kindly leave the stage!"

LoL [or not]

~M~

& of course Al is absolutely right too above about the ontological significance ~~ and existential and epistemological to boot...