aakk9999 - 10:55 am on Apr 23, 2012 (gmt 0)
Depending on the number of reviews, what about each site having around 1/2 reviews on page and the second half in iframe stopped by robots?
So both pages show all reviews to user, and both pages have on-page review content (half of reviews), beefing up the page content, but there is no duplication.
E.g. one site shows reviews 1, 3 and 5 on-page and reviews 2,4,6 in iframe. The other site does it other way around.