They really don't even need to go to that extreme unless they really want to include 4-lane songs in the tournaments. In order to maximize overall participation, they'd probably be sticking to core Blitz songs for these anyway, I'd imagine, and of the included songs, the majority of them have a Keys track. The exploit really doesn't work with 5-lane songs, at least not to the extent that makes it impossible for skilled usage of other methods to beat it.
On the topic of the tournament coming up:
Here is where you can nerf flame notes, but I still don't feel that this would be a great solution. What you should do is just ban the bandmate/flame note/xxx loadout, kind of like when Street Fighter or Soul Calibur bans certain characters for tournaments. That to me would be the quickest and most effective "fix" for the short time you have to get it running.