A littlebit "hard" solution for this but its work...
Do a cronjob @ ewery 5 minute: cp -r /var/cache/munin/www/ /var/www/virtual/YOURDOMAIN/munin/htdocs/
After the first cron run, munin available @ YOURDOMAIN/www
Secure munin with i-mscp folder protection!
This is not a good idea for many reasons