Basically what I was suggesting is you have a wall on the right and a person on the left walking to the wall for example. Make a freeze frame of the shot where the right wall is not obscured. Then overlay that over the footage with a linear wipe and a feather that cuts off just about where he intercects the wall and then his plate should seem to disappear underneath the piece of wall.
It’s not ILM but it should get you started.
Does this make sense?
Andrew