I think the OBi might be able to perform this trick with the new firmware v1.3. Since we can record prompts to the IVR, we should be able to send numbers with no CID to the Auto Attendant. Since we do not leave any instructions to press any buttons the caller should simply hear our message saying "We do not accept calls with blocked CID, you must unblock your number" (or something to that effect). If you use this work around method, you will give up on the ability of using the AA prompts in your language of choice. However the options of pressing 1, 2, or 3 are still there, they are hidden. The options are just not known to the caller. I'm not sure what the AA behavior is if the caller does not hang up. I think the AA repeats three times. After the last repeat I'm not sure if it just disconnects.
RonR is better at figuring out a dialplan which will force callers with no CID to the AA.