Hmm, wow... yeah. The only thing I can think of is motion controlled camera (on a crazy crane) on a guy fake(?) running on a piece of heavy plastic(glass) hanging in a completely surrounded green screen. Or maybe it becomes photo real cgi when it get's below his feet?.?.? If they do use motion controlled cameras, you could splice an above glass shot, with a below glass shot perhaps.
To me, it definitely looked like a 3D model of the runner cut together with live footage of him. the live footage was when he was running through the park, and down the stairs. I believe the rest was a 3D runner.
The strength in the Milo motion control rig is the ability to export the camera move as a file and use it in your favororite 3D app, applying it to your camera. Makes for seemless match-moving with no need to track anything.
The running on pexiglass was a neat touch. Don't see that very often.