After years of rolling a mod wheel to get vibrato on pretty much any device, I miss this functionality with the MidiNES (since the mod wheel changes the pulse duty cycles).
To get vibrato, I've just been sloppily drawing saw waves with CC 08 (or assigning a knob to CC 08 and recording my craptastic knob twiddling by recording over the existing midi track).
Is this the typical method, or is there another way? CC 08 can be a bit... unpredictable, so it takes a lot of screwing around to get plain vanilla vibrato, at least in my experience.