If you really want to be able to automate the send with a button, you can route it through an Aux track to the bus, and automate the Aux track's Mute or Input Echo. It's trading 'clutter' for convenience, but I thought I'd mention it.
As for whether this is a 'standard' feature, I did a quick search, and immediately found forum posts indicating this isn't possible in Logic Pro or Harrison Mixbus, either, so SONAR's not alone, though it might be in the minority. I also failed to find a request for it in the Feature Request forum and only a handful of other posts about it over many years, so apparently it's not missed that often.
Every DAW has it's own set of unique or unusually-implemented features and ways of doing things; you get used to the features you have, and generally don't miss the ones that aren't available. When you run into that one missing feature that seems like a gross omission, you have to keep it in context. Every time I've tried another DAW, not an hour went by before I was banging my head against a virtual wall, trying to do something that's a cinch in SONAR.