Steps
Frontend
Backend
Side
Frontend
Either you manually change your API paths, overload them step by step, or use a router like ApiMock.
Backend
You need to serve the JSON to the frontend, but also keep it as documentation for the API implementer.
Do this with a fake server like Interfake, or create a real server with Express, or just host your files statically.
Side
A sample JSON file works as documentation, but a JSON Schema is a better option.
You can create sample data from a JSON Schema.
You can create a JSON Schema from sample data.
Tip: Do one sample (like one search result), generate the schema from that, then generate as many samples you need.