Yeah. The pitch plugin is capable of this.
Two midi tracks each with a different vst instrument and two scale plugins on each channel (which can now be made a .adg).
The first pitch plug in the chain will define the notes on your controller that are allowed to pass through to the second pitch plug. The second will define what octave to actually play on the vsti by adjusting the semitones in multiples of 12 (+ or -).
Say for example you have a two octave controller and you want one octave to control one synth and the other octave to control the other. (C1 and C2)
So on your first pitch plug on your first midi channel will be set to C1 with a range of twelve and then you can adjust the octave you want to control on your synth with the second pitch plug.
Then set your octave on the second for C2. Adjust second pitch accordingly.
Here is a device group that will work in v5.
http://www.experimedia.net/ableton/pitc ... lsplit.adg
Making a plugin dedicated to this would be redundant.