You could leave your shirt untucked so it covers your waistband then people would be so busy thinking did @tim get dressed in a rush/in the dark they wouldn’t notice the pump up your jumper.
I sometimes put my pump clipped to my waistband but inside my waistband against my stomach. Only possible if your trousers/skirt aren’t too tight, you still get an oblong lump just no one can see what it is.