Easy peasy. This was a pretty simple hack, but it’s a good place to start.

From here, you could obviously go crazy with complicated Arduino setups, but you could also modify the source code of MyoDuino itself. The Myo Armband has a built in 9-axis IMU that normally captures arm motion, but isn't being used here. By expanding MyoDuino you could create motion gestures to really open up your control options.

You could also build your own pose “edge” behaviour, like you see in Myo Scripts (Meaning that you get one event when a pose is started, and another when one stops). As it stands this will keep setting the relevant pin to HIGH over and over as long as you hold a pose, which may not be ideal for your application.

Finally, if you want to enable casual usage you could tweak the locking behaviour so it won’t lock you out in the middle of a pose.

That's all beyond the scope of this guide though! If some of those ideas sound interesting to you, you can get started at http://www.myo.com/makers