If you're a programmer, you could use the LR SDK to write a plugin script that creates collections based on the folder structure. Adobe hasn't provided SDK documentation for LR 4 yet, but there doesn't appear to be many changes from the LR 3 SDK, so its documentation should be adequate. The learning curve can be a little steep, so expect to spend at least 6 hours, perhaps more, depending on your facility at picking up new programming languages and applications.
Thanks, John. Do you have a pointer to a Mac version of the LR SDK, or a 4.0 version?
The only thing I see on Adobe's site is this link:
but it's for version 3.0 of the SDK, and then on Windows only.
That download is mislabeled -- the SDK is for both Mac and Windows. (The SDK is just documentation plus samples.) As I mentioned, the LR 4 SDK hasn't been released by Adobe yet, but the LR 3 SDK should be good enough.
Thanks, John. LR3 SDK works OK with LR4 on the Mac.
Now, on to that steep learning curve part. . .