S3 Add header when copying files

I am using knox to copy files between two folders of the same bucket and I need to maintain the same source headers and add a Cache-Control header in the destination file. The only way I found is:

1. list all files in the folder


2. make a HEAD call to know the Content-Type of each file in the folder


3. 
   

   make a copy operation with these parameter:

   
   

   
   var headers = {
     'x-amz-metadata-directive': 'REPLACE',   
     'Cache-Control': 'max-age=2592000000',    
     'Content-Type' : variable 
   };
   aws.copyFile(source, dest, headers, callback)
   
   

The x-amz-metadata-directive is needed because of the default copy just keeps the source metadata. Is there an easier way to add a metadata (even after a standard copy)?