Easiest way to think about backside corked 540 it is like this:
1) Spin by throwing lead shoulder into rear binding. That's what starts the off axis spin.
2) Grab mute (lead hand on toeside of snowboard, between feet) to lock in the rotation.
2) Landing is tricky part. The landing should come into view at about the 360 mark and depending on how much you corked, you'll have to look upwards as well to spot the landing.
The more corked you go, the more you'll have to look upwards to spot the landing as you come out of the corked rotation and land on your feet again.
Here's what it looks like when I do one (it's regular so you have to mirror it for your goofy stance):