Run the following commands in SSH as root user to install the WHM interface.
cd /usr/local/cpanel/whostmgr/docroot/cgi
wget -N http://files.betaservant.com/files/free/fantastico_whm_admin.tgz
tar -xzpf fantastico_whm_admin.tgz
rm -rf fantastico_whm_admin.tgz
After this you can finish the installation inside WHM -> Plugins -> Fantastico