Open the CSS.tmLanguage file in ST. On a mac, it's located in ~/Library/Application Support/Sublime Text 2/Packages/CSS.
Look for this part of the file
<string>less</string> <- add this line
Once you do that, when you open a .less file, you'll get pretty good color coding and all of the normal css sippets. Of course you won't get support for the less additions to css because that would require some actual work. You'll still get about 80% coverage.