With the EU background of the AT-ST pilot being an "Imperial Army Regular" trooper, I'd considered nabbing an AT-ST pilot (If they go on clearance like the officer) and somehow making him in his EU garb.
Basically, their uniform is the just the AT-ST drivers outfit, but when they're in the field (Not piloting ST's), they wear chest armor ala the officers, and have backpacks ala sandtroopers (And I'd take it a step further and say they denote simple visual rank via a pauldron like stormtroopers do).
Definately some cool 12" custom possibilities, even though it's not my particular field of interest generally. That field Officer looks great though!
12" probably has to have the most diverse list of parts and possibilities to it I'd think.