I've saw where people have mounted an axle with a wheel and tire on it off to the side of the bucket to push rolls with, but not one like you're describing. Why not look around and see if you can't find an old used 3pt unroller for a couple hundred bucks?
If you have a front spear that is the slip in type with a pin or bolt holding it you can weld a short piece of pipe heavy enough for the job on the side of the FEL. You simply move the spear to the side and spear the bale from the side and start rolling forward or backward to unroll the bale. Haven't done this but read about it somewhere. I was going to do this but we wound up buying one of the unrollers for the rear of the tractor. I planned on putting a slight forward angle to the spear mount to help it stay on better.
Front bumper with a big ro;;ing pin built in. Or for the back a rolling pin between the lift arms.
Or you could just borrow my spotter bull. I set the bale on the ground and he unrolls it. He thinks it is his job. I guess his other job is rather frustrating. :lol: