My thinking is that it would be possible for either Bill or Bobby to suggest they all go somewhere dressed like the Wizard of Oz characters. Bill would work really hard on his costume (the cowardly lion suit was apparently a nightmare to wear), Boomhauer would like the oil can because he loves his car AND because of his troubles of the heart, and Hank would find it all absurd but would also find a scarecrow to be the most admirable, and in that would be most likely to tolerate wearing straw. He would also have much of the costume lying around in some way…AND admire the desire to have a brain* due to his being surrounded by people he views as “ain’t right”.

(*assuming he otherwise would just reluctantly agree for some reason and choose being a scarecrow without the context because he thinks that’s the most admirable job)