This is possible with any class, although it's a bit trickier with heavy IMO. Crouch jump at the wall from a short distance, such that you land on a tiny bit of displacement (you can't really see it, but aim for the bit of the wall that dents inward, if you will). Adjust you position to taste, stand up, and run along the wall. Jump as late as possible without falling off, and air strafe to victory!
for airstrafe noobs: after jumping, hold W and D (forward and right) and move your mouse smoothly to the right. Your character will move in a circular arc in the air, allowing you to bend your jump around the corner. Crouching during this whole affair would be favorite.