Interesting thought.
There is no ready to use plugin available as of now that does this.
However only few browsers aside from chrome support access to midi devices yet (http://caniuse.com/#search=midi).
The definition for the browser API exists (http://webaudio.github.io/web-midi-api/), so this means It most likely is possible, but you have to write the adapter/plugin logic for C2.
Maybe some of the plugin guys can create something like that so you could use Midi input.
After all, I decided to do it myself <img src="{SMILIES_PATH}/icon_lol.gif" alt=":lol:" title="Laughing" />
scirra.com/store/construct2-plugins/midi-in-3354