Hi Scoox and niles,
While this is an older question - I'd like to add a use case:
I tend to record external synths, which as of SO5 can be created, recorded, and bounced as with VST... however - I generally record audio on a separate track using the instrument AUX channel. If I don't send that output to 'none', it doubles the signal. So I use niles' solution and create a stereo output bus called 'Null', and send the audio out there.
I do a lot of know twiddling while recording. While I can probably send custom patch-changes, and record automation channels as needed - my goal isn't to memorialize the performance midi source - but to print the resulting audio track for later mixing.
This has been captured as an KB article for SO4. If in the time since this question was asked, there are better solutions - I'd like to hear, thanks!