I want to set up a fixed with a PW Kiss Off rear hub. Can I spin a second cog onto the hub to hold the first in place? I use a rear brake, so I'm not too worried about unscrewing the cog. Well, maybe just a little.

Any advice and/or comment is welcome.

search this forum for 'loctite' 'suicide hub' , and maybe 'bumbike'
that should get you all the info you need.

Do the search like dolface said. But all you need is an English threaded bottom bracket lockring and some loctite (red I think) and the means to make them VERY tight. The BB lockring will thread right onto the freewheel threads and act as a lockring to the cog.

If you have a brake I wouldn't worry about it. I set my mtb as fixed for a while with out locktight, never slipped and almost never used the brakes. I was using a surly hub.

Use one of those narrow surly cogs so you've got all that lockring on the threads.

I'm not sure, however why you're doing this. did you find this hub on the street? Thats a spendy hub to be using in a manner not intended.