VST instruments can only respond to MIDI features, which unfortunately doesn’t support a change in volume during note playback. This is true, not only for Renoise, but all DAWs I’ve worked with, so I guess it isn’t possible ‘just like that’.
Using MIDI aftertouch to control volume would hold some promise, but unfortunately it’s not implemented in Renoise yet. On top of that, only a few VST’s support it (see this thread for a discussion)