I found a way to keep the hood down, on the commendations vendor on Hoth sells a Elder Vindicator's Headgear, for some reason when you equip it it forces the hood to turn off. Now if you want the hood to come back up go into the social options and turn off the helm display.
Partially confirmed, via the CTRL left/click preview. Unfortunately the Elder Vindicator's Headgear is Heavy Armor, and I'm incapable of wearing this piece because I'm a Sentinel. However, it indeed *appears* that wearing this piece is a solution.
Clearly this invalidates the argument that artwork would have to be redone for a /hood option to be implemented, since as far as the game client is concerned, rendering of the the hood can be easily suppressed depending on the headpiece (or in this case an eye visor).
Too bad I didn't roll a Guardian, I'd be all over this little item.