I hate to tell you, but it's never going to happen. AVI isn't a format that any major provider is using or will ever use. Roku has shown little to no interest in supporting users that want to watch their own material (they don't make money from advertising or subscriptions from that). It's not that hard to transcode AVIs into a format that Roku supports, so you may want to look into that if you really want to use a Roku device to view AVIs or use something like Plex that will do it on the fly.
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