use different config.assets.css_compressor for one css file

css_file = "compressed.css"

filter = Sass::Rails::CssCompressor.new(:uglifier)

# Output file will be compressed with uglifier
filter.compress(map_css_file(css_file))

filter = Sass::Rails::CssCompressor.new(:sass)

# Output file will be compressed with sass
filter.compress(map_css_file(css_file))