If each conductive atom of the inner conductive surface cannot collect any more electron then perhaps any other electron inside of the container to remain flying around inside. Which can perhaps add enough electrons inside to not be collected with the inner conductive surface.
The idea is not all about containing each electron on the surface of the conductive wall its about each free electron flying around inside of the container. Like a bottle that initially had a vacuum that are filled with air (atoms). Instead of filling with air can maybe just fill with each free electron to fly around inside.