Yes, the skeleton directory for all new accounts is located in /home/centovacast/system/skel.  Any files or directories you place in the skeleton directory will automatically be copied to the /home/centovacast/vhosts/USERNAME/ directory for each new account.

If you want to pre-load media, place it in the /home/centovacast/system/skel/var/spool/media/ directory.  You can optionally create a symbolic link within the media directory which points to a common directory if you wish to share a common set of MP3s amongst your streams.