I have tried multiple times to no avail. I'm pretty sure you need to eliminate most of the smaller boxes aside from 1 or 2 to let the metal box land onto the remaining crates and still leave room for you to snipe out at least one dynomite so you can blast the metal box under the platform, and then shoot the "gravity box"(Has an arrow pointing either up or down, to change shoot it) and make the metal box float back up into the target area. That'd be my best guess.
