This trick requires precise timing. Doing this wrong will cause you to fail quicker than not strumming at all. Play the notes as if it was a double note instead of a triple note. You must strum up and down at a constant rate in order to successfully do this. You must play the solo as usual, but afterwards the rest is easy. You should get at least a 90% on the song if you get 60% on the solo and do well afterwards.