If I remember correctly, Hormel (the makers of SPAM) actually did this with regards to the appropriation of their trademark to refer to unsolicited commercial email. They basically said, "Look, we'd rather you not use our trademark in a negative light, but we don't want to be dicks about it so we're granting permission anyway."
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I like the way you think. It would be great if they could offer the song files in the same way that Rifftrax does. Even better would be, you pay $1 for the click track and put your CD of the song in and the game rips it for you.
However, the game data is more than just the click track. Each song is split into several tracks so that the game can realistically model the sound when a player misses a note. CDs and tracks from iTunes aren't separated into bass, lead guitar, rhythm guitar, vocals, drums and backup tracks.
You can still play a guitar hero type game with a one-track song, but a lot of the verisimilitude is missing the moment you miss a note and don't receive audio feedback.
In order to get the multi-track version of a song, you either need to get it from the original producer or cover it yourself. For indie bands and in-house stuff, this isn't much of a problem. For mainstream songs, you need to cut a deal with the song owner, i.e. the label.
This would be taxing you based on business you're doing out of state, which would get ruled unconstitutional pretty quickly. Nice idea, though.