If your mixer has a post-fader FX loop (like the Ranes do), you can use the FX send as a direct output for deck A setting it all the way to Wet, while deck B would go out your mixer's main out setting it to Dry, then in Ableton record them separately.
If your mixer doesn't have an FX loop or it's pre-fader, that won't work. If you absolutely need ableton's Main Out to go through your mixer's channel B and Ms Pinky through A, you could consider running a Mono setup. Add a copy of this Sum to Mono rack after Ms Pinky VST's output and another after Live's, before they go into your mixer. Then, on the mixer pan Channel A hard left and Channel B hard right. That way your Mixer Main output L will be Channel A and R will be Channel B, and can be recorded separately, but you lose your Stereo Image. Also, be careful with your monitoring and routing when recording back Live's output like this, it can easily create a feedback loop. On the below pic, you'd send the Mixer's Channel B Live's output instead of a turntable.
The other (simpler) option is not running Ableton's output to your mixer, and just recording one deck of Ms Pinky as a single track, but this would depend on what you want to do. This setup works when you just want to add scratches to a track.
I'm using a Traktor Audio 6 for this diagrams, so the soundcard's Main In (front) is always line and the decks inputs can be switched to phono/line independently. I'm not sure if you can switch the Audio 4's inputs independently, but if you can't and got it working with Asio4All, you can use your Soundblaster in place of the Main In/Out in my soundcard diagrams.
