How do you remove the rear cam bearing on a small block Chevrolet engine without taking the engine out of the car?

Not easily.

First, you would have to pull the intake manifold so you could take out the lifters, and you would need to remove everything on the front of the engine so you could pull the cam part of the way out.

Then, you would need access to the back of the engine to pull out the rear soft plug, and then you could push the cam bearing into the area between the 4th and 5th bearings, crush it small enough to fit through the hole, and then install a new bearing and freeze plug.

It would be easy to get the bearing in crooked without the ability to line up the installation tool and would be hard to get the oil hole properly aligned.