Yes. In order for your movies to play on the
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TV (without hacking it, that is) they have to be part of your iTunes library, but they don't necessarily have to be stored in the iTunes Music folder on your computer. If you go into iTunes preferences and de-select "keep iTunes Music folder organized" (under the 'Advanced' tab), you can add items to your library without iTunes copying them
into your iTunes Music folder.
In other words, once you set that preference you can select 'File' --> 'Add to Library' in iTunes, then select your movies and they will be part of your library but still reside on the external drive.
Alternatively, you can leave the 'keep organized' preference selected but override that function (the organization) by holding down the 'option' key and dragging your movies into the library portion of your iTunes window. The movies will show up as part of your library, but iTunes will leave them where they are.
Bear in mind that in order for any movie file to play on the
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TV it has to conform to the supported video formats listed on
this page.