How To Inject External Javascript Code Into Other Javascript Code With a Gulp Task?

I'm trying to build an SDK that helps people instantiate and validate instances of Data Archetypes (pre-modeled JSON schemas for popular types of data).

The SDK is in one javascript file and the schemas are in .json files on github.

In Gulp, I know how to pull in external files, but what tools can I use to inject the schemas into the SDK's javascript file at this.schema in my main constructor function?

(function() {
    function SDK() {
        if (!(this instanceof SDK))
            return new SDK();
        this.schema = {};
    }
})();