Alright, here's what I've done and what I've had success with.
Device: OG HTC Incredible (4.0.3, CM9 Alpha 9)
When I installed, I renamed GoogleSearchBar, pushed Velvet.apk, then made the permissions match everything else in /system/app, after a reboot.
- Clicking the search bar will oepn the search UI. This is identical to the non-search UI in that it has the same cards appearing over time, but has previous searches from the Google account and lacks the pretty looking header.
- Clicking on the voice icon or holding down search causes it to go into dead "didn't catch that" mode.
- Clicking on the "Google" app or loading that in any way loads the Google Now UI that is presented to Jelly Bean users who access it from a home screen or from holding down the software emulated home button. I've got this as a lockscreen shortcut on CM, so it performs the same way.