How do I customize fields of a Google Guice Injected Object?

I'm currently writing Integration tests, where I @Inject the "Store" object as a private field. However, by default the injected store has the "isShopifyInstalled" set to False, making my tests automatically fail. I need to be able to set "isShopifyInstalled" to true somehow, but can't seem to Mockito.mock + Inject the Store object. Any ideas on how to set this boolean to true when Guice Injecting it?