Only via a daemon since only daemons get access to the the QCF control files containing RCPT TO: addresses.  If you are sending via the Mercury/32 queue you might be able to write something to process the "glue" headers of the 101 file to catch these.

Is there any way in Mercury (or Pegasus) to produce a failure (bounce message) to the original sender of a message that contains over a certain number of RCPT TO.

The "Compliance" tab under Mercury S module has an option for max relay RCPT, but that appears to only be incoming based on my test.