You can enable ad hoc distributed queries via heading to your Amazon Management Console, navigating to your RDS menu and then creating a DB Parameter group with ad hoc distributed queries set to 1, and then attaching this parameter group to your DB instance.
Don't forget to reboot your DB once you have made these changes.
Here is the source of my information:
http://blogs.lessthandot.com/index.php/datamgmt/dbadmin/turning-on-optimize-for-ad/
Hope this helps you.