If no seats, then sit on the floor and text your manager that you're in the office, but there's no where to plug in. Let them figure it out - that's why they make the big bucks and get the big bonuses... And personally, I'd stay there for 8 hrs, so that it counts as an in-office day.
Studies (and even WF managers) acknowledge that people are more productive when working from home, so that's not the goal here.