Now here is a real hack. As in, something that can be accomplished by hacking, with a hacksaw. Although in fact it was an angle grinder that I used to streamline my handlebars, lopping off 13 cm (5" or so).
Narrow handlebars were on-trend at this year's Tour de France, thanks to riders like Adam Hansen and David Millar. Anyway I prefer to cycle with my hands close together. My fold-up bike had what seemed to me to be excessively wide handlebars. The full width of something like 58 cm was useful for hanging shopping bags on, but otherwise something of a hindrance. By eye, 6.5 cm seemed about the right amount to cut off each end.