Unless there is a bug in their hardware implementation of AES-CCM or (shudder) some sort of crazy disclosure vulnerability in the APIs they provide, there is (presumably) no way to get at the UID. Even if you were to decap the chip and get at the UID physically, you still aren't any better off as it derives the actual encryption key on boot from the UID.

The Secure Enclave is essentially a hardware security module, in more general terms. The only thing that leaves its boundaries are the results of crypto operations, not the parameters that went into calculating them.