Adding support for multiple models

I have a (non-java-)model that successfully compiles to java. Now I want to add another model and reference to classes that were generated from it from my first model. If I do it straightforward (using string references), I get "unknown class" error for the code that references to a class from an external model (in one of model reduction steps, no text code is generated). Is there a way to reference a generated class from another model?