While in the part of the level in the tank; there's a drop in the ramp (that connects the raised free/motorway to the large warehouse like building), if you go absolutely sideways off that drop the tank should flip therefore you would appear outside it. The easiest way to go sideways is to hit the wall (head on) at either side of the ramp, the sideways tank will slide off the edge and flip. Noticeably, the future Cortez will run around manically. Also of interest is that the enemy tank inside the building only takes a few laser shots to destroy.