The size of the mirrors limits the size of the object field. For a full body you'd need extremely large and expensive mirrors. I looked up other options and saw a new technique called BOS (Background Oriented Schlieren) from 2000. It sounds like a possible option for you. It involves using a lens focused at infinity (or close to it) so the subject and background are both equally sharp. You need a busy background with lots of detail. With a locked off camera, you can use a comparison of a clean background frame with a subject on background frame to show differences in the background caused by heat and air pressure around the subject. Something like a "difference" layer in photoshop which is also available in various video editing programs will highlight any changes.
The technique is not as sensitive as traditional schlieren photography, but as it only requires a busy (noisy) background and a long lens, you can try it with minimal expense. Good luck and hope to see your results!
