Lightly wrap the wires with electrical tape.

Reinstall the cover plate.

Install the middle sleeve.

Slide the outer shell over the connector.

It may be necessary to enlarge the hole at the back of the outer shell to allow it to fit over the taped wires.

Wrap electrical tape from the back of the shell down the wires until it extends about 5 cm, reducing the overlap as you go. This will act as a poor man's external strain reliever.