It appears you can just change the snippet to say "rating=5 star" but is there a way to collect reviews and aggregate them into the rich snippet?
The best way to achieve rich snippets is by marking up your web pages with schemas, which provide better semantics to your website, overall, and also informs Google Search about the structure of your contents.
You should work with your Web developers to build a feed of your all your reviews that can simultaneously feed your schemas. But you cannot fake your reviews, you cannot have 5 stars because you defined it that way, it has to come from customers feedback. Such feedback comes directly from your site, Google Places, and other public pages where your customers can leave a testimonial (Yelp, Foursquare, etc.)
This means that you will have to prepare both your own website for receiving feedback, but also create a positive business reputation across different places online that customers can use to provide testimonials and rate your services.
Google Search has worked on providing support for businesses without physical location. I suggest reading through their guidelines at the Webmaster Help & Support Center.
Yes, for example Signs.com is a commercial printing company that aggregates the reviews across their site into an aggregate review rating that shows up on every page of their site. A bit of a gray area since in the search results they make it seem like every product has thousands of reviews, when in fact that's the sitewide total.
The way to collect and aggregate reviews dynamically would need to be created by your web developer. Showing these reviews via rich snippets would require you or your SEO to work with the developer to get the proper Schema.org formatting around these aggregate reviews.
Hope that helps, let me know if you have more questions!