Here is my two cents on using a winch as a capstan.
My experience with a capstan is helping a friend who is a well driller. He specializes in fishing, and for a pump hoist he utilizes a rig is Grandfather built in 1949. It is on an International 140 and utilizes a Ford TT rear axle that has been shortened, and two capstans put on the ends. The working rope is 1" sisal, because it holds well, and can handle some burning. When your holding a 1000lbs of pipe and tooling while setting a clamp, the rope might burn a little. Because the rig is used 6-7 days a week, the capstans are always shiny. We ALWAYS throw the rope off the capstan when not in use. This is a critical safety measure. One little bur or the old opening for the winch cable grabbing the rope, or an accidental pull and the capstan is going to be sucking in rope. I can hold a 50lb piece of pipe up in the air with two wraps on the capstan, and the rope just sitting in my hand, moving my hand will raise and lower the pipe. less than a pound of force on my end causes the capstan to put out 50 lbs on the other. A rusty capstan would suck in rope, just by laying the rope on it. It would not take much for the end of that rope to be wrapped around something that it should not, like your foot. How would you spool out rope if your cannot take it off without it tightening down on the capstan? Also since your using it in a low use situation the capstan will get rusty. This will increase the friction and cause the rope to grab the capstan. Utilizing a winch as a capstan is dangerous, you must be able to flick the rope off and change number of wraps to match job.
Use your PTO winch as a winch, it will be less dangerous than utilizing it as a capstan. Capstans are amazing machines, and the amount of control they give you is nice. However you must be safe with them, don't cross your ropes, and don't leave rope on it. Some winches have capstans on the side, this would let you have the best of both worlds. Perhaps some other method utilized as a capstan would be a safer choice.