I do not mean to trivialize your problem of not being able to stream "home movies" to your Apple TV without having an internet connection. I know this is frustrating for you, as it would be for me as well. However I would have to concur with vazandrew in that, an internet connection is not needed to stream "home movies" to your Apple TV.
I ran a very simple test. I unplugged the Ethernet cable connecting my modem to my AirPort Extreme. As soon as I disconnected the cable my AirPort Extreme status light started flashing "orange". I then accessed the "computers" app on my Apple TV (which by the way is connected via wifi to the AirPort Extreme). It then loaded "my library" and I loaded a video from the "home videos" category in "my library". It played without a problem. Granted it did take a good minute or more before it actually started to play compared to it being instantaneous when I actually have an internet connection.
I then tried another experiment while still offline. I loaded an actual movie I purchased from iTunes, which is also in the "computers" app, then under "my library" and then "movies". This also played without a problem, but again it did take a good minute or two for the movie to load and start playing. Coincidently, I went to the iTunes "movies" app (again, I am still off line) and I could not connect to iTunes and got an error message to try again.
Since my "home videos" as well as my "purchased iTunes" content are all stored on my mac hard drive, I would have to agree that content can be streamed to the Apple TV while "offline". I would assume, that if I continued to watch multiple "purchased" content while offline I would eventually be prompted to "re-connect" my internet to authenticate my "purchases".
On a side note, at one point I actually stored all my purchased music and movies on a NAS drive connected to my AirPort Extreme and I ran into the same problem you are currently having where I couldn't stream anything unless I had an internet connection. About a year ago I moved all my purchased content from the NAS drive to an external USB hard drive and I haven't had any streaming problems, even while offline.
I don't know if this will help you resolve your problem. But, if this can be of any use I would at least hope it gives you the determination to continue to look for a solution because for all intents and purposes it should work for you.