It would essentially involve applying image recognition and processing techniques to the video stream provided through the Image API, but this wouldn't be a quick and easy process -- unless, of course, the object always occupied the same spot in the field of view.
If that wasn't the case, the object would need to be easily recognizable to an image recognition algorithm applied to the infrared video passthrough. (A special retroreflective sticker might work, like what zalo did in this thread).
However, if you want to take the physical solution, we recommend any dark material that absorbs infared light. Duvetyne is the absolute best for this -- it's used by Hollywood as a non-reflective material, and was actually used as the backdrop for the space scenes in Star Trek