Assigning one CC controller to multiple instruments

I'm on MS3 (latest version) with the most powerful MBP on the market. All software up to date - using many 3rd party plugs (Kontakt, Machfive, etc.)

I want to assign the mod wheel to multiple destinations: a synth's vibrato and another synth's chorus effect, let's say. It's the same CC I want to control multiple parameters. When I try to do that, MS3 automatically deletes my first mapping and only keeps my most recent mapping. This is true with all CC's I've tried.

What am I missing here? What's the cleanest way to map like this?