I flew in an underground parking structure and it was rock steady. I only lost Opti when flying too fast. I don't have any video because I was test flying without the gimbal attached. It really depends how much contrast there is on the surface for the optical flow sensor to track.
The optical flow sensor only has a range of 2.5m (~8.2 ft) so you'll be flying at the limits of the sensor. It may switch to the barometer and then the altitude holding would be less stable. Are you trying to make it hover directly over top of you from a straight down shot or will it be a little bit away from you shooting back? I'm hoping you have tall ceilings in your office becuase you'll be flying very close to the ceiling if your office is a common height.
I would not recommend doing this but in the end it's your bird, and your money.