Pompatus would appear to be a lyric from *another* much older song, misheard by Steve Miller. The word from that older song "The Letter" written and sung by the late Vernon Green, is
puppetutes--women who are half puppet and half prostitute. Green was discussing the advanatages of having "puppetutes of love."
More at Cecil Adams' column The Straight Dope here:
http://www.straightdope.com/columns/...mpatus-of-love