AirPort Extreme wired guest access
Unfortunately that is not possible, anyone with wired access to the AEBS has full connectivity, and also skips any other access restrictions or authentication for that matter.

However, you could use an AirPort Express for example to create a second guest network. When creating tgat network, you can use the same SSID as the guest network configured on the AirPort Extreme (make sure you also use the same encryption parameters and password) and clients will transparently switch to the one with the best signal reception while moving to different locations.