For now, I've updated the Review 'Instructions' text with formatting, and added the statement there.  It is now more prominent, so it's a decent workaround.  Still would like a popup or other form or acknowledgement at the time of owner approval.  

Here's what it looks like now:

Yes, we are using the review definition and the review instructions fields.  The review instructions are listed in small print and at the top - and the review definition is only shown after you click on the 'more' link.  These are great for information if a reviewer or review owner are looking for it.  What we need is a popup or check item that has to be acknowledged with the approval.

You might add a description to the review definition.  That will be displayed during the review.  You could word it something like, "By Approving this review you agree that --"