I see you've already asked on the freebsd-gnome mailing list.
Porting applications with many linuxisms and keeping the ports up to date is not always an easy task. And the FreeBSD Project doesn't have the manpower available in some Linux distributions so it might take some time.
That being said, I understand FreeBSD's GIMP port is very outdated. Just be patient, or better yet port it yourself and share the patches, if you have the skills and time.
Sometimes the maintainers need a little "push". Maybe send
them an e-mail.
If you can't wait, then use whatever already suits your needs best. Yes, this includes "live Linux CD", Windows or anything else... You're not tied to anything or anyone.