This is possible if you configure the first AirPort Extreme to "create a wireless network" and enable it to be extended.
Then configure the second AirPort Extreme to "extend a wireless network". This will provide more wireless coverage and the Ethernet ports will be enabled on the second AirPort Extrme to allow Ethernet devices to connect.
Keep in mind that the "Ethernet" connection at the second AirPort Extreme will be limited by the wireless connection quality between the first and second AirPort Extremes.
So, limiting obstructions in the wireless signal path between the first and second AirPort Extremes will be very important for a good quality connection.