Creating additional address on a corner property?

[Mark Sandvig]

I own a mixed use property on a corner lot in St. Louis (Tower grove area). There are 2 commercial spaces and 2 residential spaces on the property. There is a good-sized garage in back that I am considering converting into a 1 BR apartment. The trick is that the entrance to this property (if converted) would be from the side street of what the official property address is. Does anyone know how I would go about getting an additional address on the side street? In other words, it's not as simple as just adding a B or a C as is common in units that all face the same street. 

Any recommendations would be welcome!