I think it is a great idea. Instead of expensive winch cable you could use anchor rode AND it could be as long as you wanted. Unfortunately, it appears that it would take a monster, expensive capstan to have the pull of a low end winch. Something like this Lewmar C-5:
http://www.wmjmarine.com/66910202.html? ... 4Aod0mEA8wEven with the c-5, I don't know if it can grunt it out like a winch. Anything bigger may require 24V and even deeper pockets.
I hope someone has found a way to make a low end or homemade capstan do the job.