Here's my anecdotal story:
VZW Galaxy Nexus, BB 4.12. Installed everything by hand with Root Explorer after putting the necessary files on my "SD Card" (yes, I know there isn't really an SD Card). I did all the steps below all at once, not by installing parts and rebooting multiple times.
(1) Renamed /system/app/Gallery2.apk, /system/app/Gallery4.apk, and /system/app/GmsCore.apk adding .bak to each.
(2) Copied GalleryGoogle.apk and GmsCore.apk to /system/app/. Changed owner/group to root:root, changed permissions to rw-r--r--.
(3) Copied liblightcycle.so and libjni_filtershow_filters.so to /system/lib/. Changed owner/group to root:root, changed permissions to rw-r--r--.
(4) Rebooted, wiping cache and dalvik cache first. (I always wipe the cache and dalvik cache when I add or remove stuff within the system folder).
Everything seems to be working 100%, including stills, videos, pano, and bubble. I can view any of them properly in the (new) Gallery, including the bubble view.
Short form: Rename|Delete three apk's in the /system/app/ folder. Copy two new apk's to the /system/app/ folder. Copy two new library files to the /system/lib/ folder. Fix group and permissions. Reboot. This is only accurate for a VZW Galaxy Nexus running the 10/30/2012 Bugless Beast ROM.
Some notes, particularly with regard to the VZW GN with the BB 10/30/12 ROM.
(1) My 10/30/2012 BB ROM (the latest) had both Gallery2.apk and Gallery4.apk. I have no idea why, and only one "Gallery" ever appeared in my app drawer or any app listings. Not knowing "any better", I renamed both of them by appending .bak to make sure neither was recognized by the OS, but left them in the /system/app/ folder for easier restoring in case the installation turned out to be a disaster (it wasn't). If I remember I'll drop Pete a note asking why there is both a Gallery2 and Gallery4 in his BB ROM.
(2) My BB ROM already had a libjni_mosaic.so, and it was identical to the one provided in the original 4.2 Camera update, so I did NOT bother to update it.
(3) My BB ROM already had a GmsCore.apk, but it was NOT the same size as the one provided in the original 4.2 Camera update, so I DID update it. The updated one is considerably larger, and it has a nice custom icon as well. (No it doesn't show in the app drawer)
(4) There is apparently a slightly patched version of the Camera 4.2 apk that removes the check to see if the device supports it. (4.2Camera_t02.zip). Since I am using an approved device, I did NOT use the patched version, just the "stock" leaked version of Camera 4.2.
ymmv, this is just my version so far of the Camera 4.2 leak story...