You could also shape a clothes hanger to fit into a pair of gloves to set them into the arrangement, as well as a cane.
I would make it big tall and what the biz calls "airy". You probably want this to be something to remember.
Like Rose, I immediately thought of flipping the hat over and doing the arrangement inside it. Make sure you use another container inside to hold the water.
If blue and white are the colors you go with try delphinium, irises, and statice for blues....these are line, focal and filler flowers in order.
You can also go with mardi gras colors seeing as jazz is linked with New Orleans...these are purple green and yellow/gold.
Or just whatever colors the co-oridinator for the function has picked out.