I’d second @dkmayer’s suggestion 
so now I’m sending MIDI from SC->Ableton->MASSIVE.
With VSTPlugin you’re much more flexible, because you can also directly control all VST parameters in the Language and/or Server and do really wild stuff. Give it a try! VSTPlugin v0.3.3 released!
but I go it working with channel-wide afterTouch messages; this will allow me to just create more midi tracks with Massive, but I still want to figure out how to get it working with a single instance of the Massive synth.
If you’re using several MIDI channels, why not use pitch bend in the first place?
Also, with SC + VSTPlugin you can easily spawn as many Massive instances as you need, so you could use a single instance per voice and simply tune the oscillators as fast as you want. You can also easily extend your idea to other parameters, like individual filter curves per note. On the other hand, it’s also very easy to simultaneously set parameters for several instances. SC is much more flexible and powerful than a DAW in this regard.