Sidechaining an insert from a bus

Hey all,
 
I thought this was possible but somehow it's not working for me right now. I'm using Waves Vocal Rider. Usually I let it run a mild pass by itself, writing automation and then I adjust manually. But the recommended method is actually feeding your mix (sans vocals) into its sidechain input so that it can better judge when to boost and cut volume. So, thinking to try this out, I created a "premaster" bus with everything but leadvocal, a leadvocal bus with just leadvocal, and a master bus to sum the two. I now want to create a send from my premaster bus to my Vocal Rider (either on the leadvocal bus or the source track), but it doesn't show up in the list of available destinations. I can only create a send directly to another bus.
 
Am I doing something wrong or is this really not possible? That would be disappointing for a number of scenarios, not just this one.

I don't have any Waves plug-ins to test but have used other plug-ins using a similar routing with no problem. The only time a bus cannot send to another bus is when it creates a loop.

Hey Scook! I'll review my routing again. But to clarify, I'm not sending to another bus, I'm trying to place a send on a bus and direct it to a sidechain input on a plug. This doesn't seem to work for me regardless of whether said plug is on a bus or a track.

Pwalpwal, I don't have another DAW that supports VST3 side chaining. But I side chain Waves plugs all the time. Even in this project. I just can't seem to be able to do it when the source is a bus. In fact, none of my other side chain destinations (e.g. FabFilter Pro-C and Pro-Q2) show up either when trying to create a send on a bus.

I'll review my routing then. Thanks for checking, Scook!

And yeah I use VST3 exclusively for my Waves stuff. Plus my FabFilters didn't show up either so it can't be that. I bet it's a dumb routing mistake. I'll be back when I figure it out!