OpenFilePanel alternative

Hello, I am in need of opening a file from the explorer in my Unity project.

The code I use now is the following:

 string newFilePath = EditorUtility.OpenFilePanel("Select JSON file", Application.streamingAssetsPath, "json");
                 
 //Debug.Log ("Game is loaded with this level: " + newFilePath);
 if (newFilePath.Length != 0) {
     JSONLines = "";
     filePath = newFilePath;
     StreamReader reader = new StreamReader(filePath);
     while ((line = reader.ReadLine()) != null)
     {
             JSONLines += line;
     }

This obviously does not translate to a standalone build because it is EditorUtility.

Is there a way to make this happen in a standalone build (let the user select a JSON file and return the content as a string)?

PS: I have looked at the UniFileBrowser offered by user Eric but if it is not too much of a hassle I would rather have it non-paying.

PS2: I took a look at this http://wiki.unity3d.com/index.php?title=ImprovedFileBrowser but I am completely lost in how to get this working (if it even can do what I want).

Thanks a lot for the help in advance, Dennis