This works for me,
# BEGIN WordPress
RewriteCond %{QUERY_STRING} !s
RewriteCond %{HTTP_COOKIE} !^.*(comment_author_|wordpress|wp-postpass_).*$
RewriteCond %{HTTP:Accept-Encoding} gzip
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /(.+)(/?)\ HTTP/ [NC]
RewriteCond %{DOCUMENT_ROOT}/wp-content/cache/supercache/%{HTTP_HOST}/%2/index.html.gz -f
RewriteRule ^(.+)$ /wp-content/cache/supercache/%{HTTP_HOST}/%2/index.html.gz [L]
RewriteCond %{QUERY_STRING} !s
RewriteCond %{HTTP_COOKIE} !^.*(comment_author_|wordpress|wp-postpass_).*$
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /(.+)(/?)\ HTTP/ [NC]
RewriteCond %{DOCUMENT_ROOT}/wp-content/cache/supercache/%{HTTP_HOST}/%2/index.html -f
RewriteRule ^(.+)$ /wp-content/cache/supercache/%{HTTP_HOST}/%2/index.html [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
# END WordPress