Render a poly wav from Audition?

Actually this is relatively simple to do in Audition's Waveform view, and probably a lot more flexible than attempting to do it in Premiere. The key to the whole thing is to create a carrier for your new file in exactly the format you want it. What you have to do is copy and paste what you want from your existing file into the new one in the correct format - you can have them both open at the same time in Waveform view. The starting point is this:

If you look at the bottom line, it says 'Custom'n and here by clicking on the twirl-down you can alter the naming of the channels to suit whatever you want - even just a number:

After this it's a straightforward cut and paste exercise. (If you missed it, just out of sight to the right of the - symbol is the + one for adding channels)

You might be able to do this in Premiere.