Yes. You don't have to have a location to have reviews displayed as a rich snippet in search results. There are a number of resources you can use. Schema.org can help you learn how to markup your HTML so that Reviews are labeled properly.

This site makes it even easier by populating the code for you: http://schema-creator.org/review.php

Once you have your code, test it with Google here: http://www.google.com/webmasters/tools/richsnippets

To learn more general information about reviews, visit: https://support.google.com/webmasters/answer/146645?hl=en

Keep in mind that even if your code is accurate, Google might not display the snippet in search.