Doghead's method gets my vote for sure. I'm pretty sure that it's common knowlege that somewhere, some time, some how... Someone, even someone who knows better, will run the winch by themselves.
There is a LOT that can go wrong. The big key you need is patience. The second is diligence. Otherwise it's not "if", but "when" an appendage is removed. Hopefully it's removed from the truck and not you.
Make sure the PTO lever is tight, the linkages are tight, and the gate is dead nuts accurate. TRY YOUR HARDEST to get the lever in gear and "tease" it back and forwards to see if you can clip the gate over it without getting it fully into neutral. It should be fool proof. Once it's fool proof, you can use it as a second opinion for your first hand observation that the winch is indeed in neutral.
Make sure the winch is in top shape. Every part of it should work properly, the drag brake, and the drum clutch latch become even more important if you're on your own. (I notice that I see more winches without a drum clutch latch than with them, including mine. There needs to be an alternate solution and it needs to be a positive failsafe solution.
You should find the oportunity to winch something just for the sake of doing so, WITH assistance, and take the opportunity to be in both jobs. In the cab, and outside the cab. Know and be familiar with the sound and feel of a properly working winch, a properly winding cable, etc. You won't be able to pick out something that's wrong until you know what's right.
Don't be too complacent to make the effort to get in and out of the truck. Tie a rag on the cable about five paces or twenty feet out. Never let that rag out of your site. When gets near your line of site at the hood, it's time to check the wrapping. At that time, move the rag out five paces again.
Know where that rag disappears from view. Know exactly how your winch chain fits into that distance. Be sure you are able to stop your winch BEFORE the chain wraps around it. It will not even slow down, the only noise you'll hear is the exensive one. Keep a small bar to stick into the u-joint at the worm gear, wind the last couple of turns by hand.
DO NOT BE COMPLACENT. It's a pain in the butt, you feel like you're running back and forth more than you are winching. That's as it should be, to remind you you're doing what should be done with two soldiers... The winch and PTO mechanism are NOT inherently fail safe devices, they are metal, cold, unfeeling, uncaring, and unbelievably strong devices that just don't care. You can not task a machine like that to babysit a wire rope, which is cold, unfeeling, uncaring, only "believably" strong, and broken or otherwise, if given the chance will sometimes throw a temper tantrum.
YOU babysit the wire rope. YOU babysit the winch controls. YOU babysit the bystanders who don't understand the dangers of winching. YOU babysit the bystanders who think they know enough to help but actually don't. And when you get a break in that, THEN you get in the truck truck and operate the thing.
Really, honestly... It is so much easier and depending what you're up to it's often faster to hold off and recruit an extra pair of hands.
I'm beginning to think he was talking about another type of winch. Whatever the case I hope I never find myself in a situation where I have to winch alone. 
