I wouldn't accept that location, with or without a post . As far as im concerned, they messed up, not you. If they have to get all new lights (because now the cords are too short), that's on them, and you shouldn't have to pay for their mistake.
If they are 12V lights now, and If they agree to replace the lights, tell them you want 120V lights w/GFI . Then you will be able to run them independently of each other. GFI breaker is much cheaper than buying multiple xformers.