UPDATE: doesn't seem like it's possible... truenas/sg_ses doesn't see the enclosure at all when the card is in IT mode. :(
I installed it via the deb file so that I don't have to mess with restricted apt
permissions truenas comes with.
To download: wget http://ftp.de.debian.org/debian/pool/main/s/sg3-utils/sg3-utils_1.45-1_amd64.deb
To install: dpkg -i sg3-utils_1.45-1_amd64.deb