The straight forward way to do so is running DeleGate with the privilege of the super-user (with OWNER=root). But running DeleGate under the super-user's privilege is not recommended in the consideration of security. You can escape the problem by installing files under DGROOT/subin/.
For example, the command subin/dgbind is invoked from DeleGate when a privileged port is required as -P80, or to bind the source port of a FTP data-connection. A file descriptor of an unbound socket is created by DeleGate and inherited to dgbind with the argument indicating the port number to be bound. On the invocation of dgbind, the effective user-ID of the process is set to the one of the super-user (root) so that it can execute the bind() system call for privileged ports.
Those executable files in subin is created automatically when you created DeleGate from the source distribution. They are available in the binary distribution for several platforms too.
To let the executable files in subin, dgbind for example, be executed with the privilege of the super-user, let the files be owned by root, and set the "set-user-ID-on-execution" bit and the "set-group-ID-on-execution" bit.
# chgrp group dgbind