How to route Ableton audio out on the 4th fader on NI S4?

So, from now on, I am a proud owner of Native Instruments S4 and Novation LaunchPad Mini. :cool:
I was thinking to buy Pioneer, but, as a Traktor user for more than 12 years, i didn't like the Pioneer ecosystem at all.
I think the RecordBox software looks like a Virtual DJ with Serato skin... :thumbdown:
Anyways.

Now, I have a question. Sorry if i sound lame.

How can I route the audio coming from Ableton in to the S4 channel 4 (the fader for deck D) ?
Thanks in advance :)