I’m quite surprised this feature isn’t there. I’m not sure if you can import your own “drum” samples, but if so, it might be possible to sneak in a stereo mixdown that way, and trigger it from the beginning… just a thought, I haven’t tried.
For my part, I would like it so I can record into SD3 standalone, because standalone has no problem with CC4 for the hihat controller; whereas in my DAW, I have to fiddle with a few things to get it to send the values to the VST plugin (and I always forget what sequence of it works – ends up taking me about 5-10 minutes of stumbling to get it to work).