Aaargh - that seems to be a Solo vs. Performer issue: Performer has the ability to send MIDI commands on bindings (“Triggers”), something that’s apparently missing in Solo.
So unfortunately, you’ll be out of luck using bindings - you’ll only be able to control VST parameters with them in Solo - and since VB3-II doesn’t expose the A/B switch as a VST parameter, this won’t work.
So I guess you’ll actually have to use notes to switch A/B - you could use a separate route from your mixface to VB3-II that doesn’t get transposed. Might require a bit of re-organizing your MIDI port setup.
Or you could upgrade to Performer and get all the benefits like pre-loaded setlist, shared racks etc - definitely worth it!