As the ebuild of glftpd configures a basic version of the program it would be helpful to make it more flexible with help of USE-Flags such as "jail" or "tcpd". At the moment jailing is predefined and only changeable via script "/opt/glftpd/installgl.sh.orig" or editing the ebuild prior to emerging it.
Feel free to submit a patch. I don't really understand what kind of "flexibility" are you asking for. The chroot is not optional, that's how glftpd works (see install docs).
