Title says it all. Is this Less option:
http://lesscss.org/usage/#command-line-usage-source-map-map-inline
Available via grunt-contrib-less, or some other plugin
It sure does, here's a stripped down config of what I use:
less: { options: { sourceMap:true, outputSourceFiles: true }, lessFiles: { src: [ '*.less' ], ext: '.css', cleancss:true } },