In DC alternative energy applications PWM's are often used to control the charge rates on batteries. I have not heard of the use suggested, but it does not mean that it is not possible.
Sounds to me like it is an engineering problem as it is unusual and should be taken to an engineer willing to take it on as a project, but that will involve a good deal of money. Or in otherwords, off teh shelf I have not heard of something that will work, unless I did not understand what you are trying to say.
