How can I use LESS in a subtheme in Drupal 6?
I am looking for a cleaner answer to this as well but I have found I need to create a main.css.less file in the subtheme and copy all the references which use the new subthemes variables (lib.less) and then they work. 

Without copying the main.css.less into the subtheme the new variables don't work. 

Maybe this is the correct way, but it doesn't feel right to me.