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.