There is now a way to run Plex on your Apple TV without a jailbreak. It just requires a clever hack and some use of the Apple’s movie trailers app.
It’s pretty straightforward for folks who want to use it.
Here’s a note:
In order for PlexConnect to work the ATV has to have its DNS server changed to that of the ATV, in order to ensure that the device’s IP does not change you need to need to either set a DHCP reservation or static IP in your router for the device and then make a note of it. Click here for a Lifehacker guide on how to set this up.
1) Download PlexConnect (links below)
2) Go to “Settings” on your Apple TV.
3) Then to “General.”
4) Next, choose “Network.”
5) Then to “Ethernet.”
6) Choose “Configure DNS.” You will want to write down the number:
7) Choose “Manually” under the “Configure DNS” screen.
8) Here, you should change the IP address to that of the device you are running PlexConnect on. Click on ‘Done.” Here’s something mentioned by the instructions:
If you are using a firmware prior to 5.2 and it asks you to configure the IP address of your router and the subnet mask leave them as they are.
9) It takes you back to the Ethernet Configuration screen. Just make sure that DNS server is set to manual, and that the IP address matches that of the computer you are running PlexConnect on.
For more information on configuring and installing PlexConnect, you can check out this guide: Link