Adding the company to Google Business
You can add the business to Google Business which provides the data to Google Plus, Google Search and Google Maps. You will need to provide the actual address for verification purposes and you can disable the address being shown by clicking the checkbox
I deliver goods and services to my customers at their location and this will hide the address. Google also does not allow PO boxes or any other type of forwarding address.
Real businesses do not hide their address
You should try and convince your customer that it is in their own interest that they display the address. No one wants to deal with a company that has no VISIBLE trading address, no return address, no complaint address or hiding behind a PO box. Its shady and less reputable to both Google and customers.
- Businesses without a visible trading address will not benefit from citations or backlinks on various reputable sites i.e Yelp, HotFrog, Yell etc.
- Customers will not be able to leave reviews on citation sites that can directly and indirectly improve search rankings.
- Customers will not be able to find their business on Google Maps, obviously because they don't have a location to display.
You only options are to increase the organic search ranking which means good content and real backlinks. You wrote
I'm trying to create backlinks for them. , you should be aware that Google has laid the smackdown on user generated links and Google has had the ability to detect such links for awhile now.
Creating links that are not natural will hurt your customers rankings in due time.