My first concern is that the tail is wagging the dog.  Protein is only a small part of the total equation for feeding cattle, and you are looking at making a large commitment for a total system that will maybe not be there a year from now.  Feeding fat to cattle has its place, but like any other non traditional ingredient, you need to be careful how you use it.  Generally, introducing fat to cattle should be done gradually, which rules out buying thins and trying to put weight on them, unless you want to mess around with about five or six different pens so you can move them through as they adjust to the ration.  The second concern is palatability.  Cattle don't really like to eat meat products unless they are well mixed with something else, so I don't think you are going to be happy with the results if you try to add it to junk hay.  If you have some corn silage you can probably do it, but there will have to be more than CRP hay involved.  Darwin Braund used to work for Agway at their research farm.  He said when they tried to feed meat products to a research herd that was used to having new ingredients in their feed on a regular basis, "It was the first time I ever saw a cow actually gag".

There are very real limits on how much fat a cow can handle.  If the product you are getting is not consistent you are going to have to adjust your ration almost daily or else set it so that the limit of meat fed is based on the highest fat product in the mix.  If you don't have any experience in feeding cattle, this seems like a fairly complicated way to jump into it on a rather sizable scale.